Glossary of Insulator Terms

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This glossary contains the following information:

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A

ANSI
Abbreviation for American National Standards Institute.

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B

"Baby Battleford"
Nickname for CD 734.8.

"Baby Columbia"
Nickname for CD 262.
See also: Columbia

"Baby Signal"
Nickname for CD 160.
See also: Signal

"Baby Teapot"
Nickname for CD 791.
See also: Teapot

"Baby Wade"
Nickname for CD 721 and CD 722.
See also: Wade

"Ballerina"
Nickname for CD 298.

"Barclay"
Nickname for CD 150.
See also: Spiral Groove

Base
The bottom of the insulator; generally what the insulator would rest on if placed on a flat surface. The base may have drip points on it.

"Bat Ears"
Nickname for CD 321 and U-389.

BE
Abbreviation for Base Embossed. Used to denote that there is embossing on the base of the insulator.
See also: Base

"Beal's"
Nickname for CD 309.

"Beehive"
Nickname for CD 145. May also refer to the Canadian "Beehive" CD 143, as well as porcelain U-132 through U-153 and U-157 through U-160.
See also: Grand Canyon

"Bell Chambers"
Nickname for CD 317.5. Used in conjunction with the Wing Chambers CD 124.5.
See also: Candlestick, Chambers Companion

"Big Mouth"
Nickname for CD 128.4.

"Bird Feeders"
Nickname for Battery Rest Insulators.

"Blackburn"
Nickname for CD 141.6.

"Blob Top"
Nickname for CD 126.

Blotted Out Embossing
Old embossing on a mold that was attempted to be removed; however there are traces of the old embossing still visible. Do not confuse this with ghost embossing.

"Boat Anchor"
Nickname for large, heavy multipart porcelain insulators, such as the M-4800 which weighs 55 pounds!

"Boch"
Nickname for U-928 and U-928A.

"Boston Cable"
Nickname for CD 266, U-408, and U-408A.

Bracket
A wooden or metal mounting device designed to fit in the pinhole of an insulator, and attach it to a (normally) vertical surface such as a pole or the side of a building.
See also: Pin

"Braille"
Nickname for the CD 113 from Canada that has dots on the skirt that appear like braille.

Brass Bushing
A threaded brass insert that was inserted into the pinhole while the glass was still molten. This created perfect threads to assure uniform contact with the pin and protect against pin expansion. Sometimes referred to as a liner or thimble.

"Bullet"
Nickname for several styles, including CD 132, CD 133 and CD 133.4.

"Burbrook"
Nickname for CD 149.

Bushing
A cylindrical insulator with external ribs on one end usually mounted on a transformer and used to insulate high voltage leads.

Button Mold
A three piece mold where the mold line for the dome piece was raised up from the typical location at the widest point of the upper wire ridge. This created a circular mold line, sometimes called a "button", high up on the crown.
See also: MLOD

"Buzby"
Nickname for CD 141.8.

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C

Cable
A large diameter line wire that often rests in the saddle groove.

Cable Insulator
A larger insulator with a saddle groove designed to support a heavy cable.

"Canadian Boston"
Nickname for CD 136.4.

"Candlestick"
Nickname for CD 317. Used in conjunction with the Chambers Companion CD 132.4.
See also: Bell Chambers, Wing Chambers

Carnival Glass
Carnival glass is a coating which is applied as a liquid and sprayed onto the hot glass when it is slightly above 1100 F. The liquid carrier evaporates with the heat, and the result is a deposit of a metallic coating on the glass. The color can range from a dull orange brown on some Hemingray insulators, to a bright "marigold" carnival on many of the Pyrex pieces.
See also: Flashed Amber

Carrier-circuit
High frequency (30,000 cycles per second) long distance telephone lines used to carry hundreds of telephone calls on the same line.
See also: CM, CS, CW, CSA, CSC, CSO

Casting
Seldom-used form of making wet process porcelain insulators where a difficult shape is desired. Thick clay slip is poured into a plaster mold. The plaster mold absorbs the excess water leaving a semi-dry clay body.

"Castle"
Nickname for CD 206.

CB
Abbreviation for Corrugated Base. Used to describe the type of base the insulator has. A Corrugated Base has fine cross hatching making it slightly rough.
See also: Drip Points, Base

CD
Abbreviation for Consolidated Design Number, a system for cataloging the shapes of glass insulators.

CD Number
Abbreviation for Consolidated Design Number. CD numbers are used to identify different shapes of glass insulators, regardless of manufacturer or style number. An example of this notation is "CD 154". A more complete discussion of CD numbers can be found under CD Numbers Explained.
See also: M-number, U-number

"Chambers Companion"
Nickname for CD 132.4. Used in conjunction with the Candlestick CD 317.
See also: Wing Chambers, Bell Chambers

"Chester"
Nickname for CD 123.2.

"Chicago Diamond Groove"
Nickname for CD 135.

CIC
Abbreviation for Canadian Insulator Collector. For more information about this insulator magazine, see the Canadian Insulator Collector listing.
See also: CJ, RR

CJ
Abbreviation for Crown Jewels (of the Wire). For more information about this insulator magazine, see the Crown Jewels of the Wire listing.
See also: CIC, RR

"Claw"
Nickname for CD 109.5, CD 206.5, and U-184. May also be referred to as "Harloe's Claw".

Cleat
Refers to various styles of porcelain house wiring insulators often composed of two porcelain halves used to clamp two or three low voltage wires in separate grooves. These insulators were secured to wooden rafters and walls with either screws or nails in holes formed in the insulator.

"Climax"
Nickname for CD 184.

CM
Marking found on certain insulators specially designed for high frequency (30,000 cycles per second) long distance telephone lines called carrier-circuits. The "C" stands for Carrier-circuit application and the "M" denotes the insulator was intended to be used on Mid-span installations.
See also: CS, CW, CSA, CSC, CSO

"Cobalt Blob"
Nickname for CD 140.5.

"Columbia"
Nickname for several styles, including CD 262, CD 263 and CD 264.
See also: Baby Columbia

"Combination"
Nickname for M-2795 (Combined glass and porcelain).

"Combination Safety"
Nickname for CD 139.

"Confederate Egg"
Nickname for CD 701.6 and U-970.
See also: Egg

Consolidated Design Number
Consolidated Design Numbers are used to identify different shapes of glass insulators, regardless of manufacturer or style number. A more complete discussion of CD numbers can be found under CD Numbers Explained.
See also: CD, CD number, U-number, M-number

"Coolie Hat"
Nickname for CD 304; sometimes simply referred to as "Coolie".

"Corkscrew"
Nickname for the large CD 110.6 and the small CD 110.5.

CREB
Abbreviation used by some collectors for CRown Embossed Brookfield.
See also: crown

Cross-top
Refers to insulators with two top cable grooves that cross perpendicular to one another. This feature can be found on CD 141, CD 204, CD 208, CD 244, U-432, U-432A, U-923 to U-923E, U-927A, U-927B, U-942, U-954A, U-954B, U-954C, U-958, M-2105, and M-2111.

Crown
The section of the insulator from the upper wire ridge to the dome.

"Crown, The"
Nickname for CD 268.

CS
Marking found on certain insulators (CD 128) specially designed for high frequency (30,000 cycles per second) long distance telephone lines called carrier-circuits. The "C" stands for Carrier-circuit application and the "S" denotes the insulator was intended to be used on a Steel pin.
See also: CM, CW, CSA, CSC, CSO

CSA
Marking on CD 128. The "C" stands for Carrier-circuit application and the "S" denotes the insulator was intended to be used on a Steel pin. The "A" has no known meaning. These insulators were made of boro-silicate glass such as Pyrex glass.
See also: CM, CS, CW, CSC, CSO

CSC
Marking on CD 128. The "C" stands for Carrier-circuit application and the "S" denotes the insulator was intended to be used on a Steel pin. The second "C" has no known meaning. These insulators were made of soda-lime glass.
See also: CM, CS, CW, CSA, CSO

CSO
Marking on CD 128. The "C" stands for Carrier-circuit application and the "S" denotes the insulator was intended to be used on a Steel pin. The "O" has no known meaning. These insulators were made of soda-lime glass.
See also: CM, CS, CW, CSA, CSC

"Cutter"
Nickname for CD 1038. This is a non-pintype insulator. A porcelain version of this also exists.

CW
Marking found on certain insulators specially designed for high frequency (30,000 cycles per second) long distance telephone lines called carrier-circuits. The "C" stands for Carrier-current application and the "W" denotes the insulator was intended to be used on a wooden pin. This designation was intended for CD 122.4 but no insulators were ever marked with "CW".
See also: CM, CS, CSA, CSC, CSO, TW

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D

Distribution
Medium high voltage power networks between customer service lines and a primary line of higher voltage.

Dome
The top part of the insulator. Also used as an embossing location designator when written as (Dome) and used to indicate the embossing that follows is on the dome.
See also: Crown, F-Skirt, R-Skirt, F-Crown, R-Crown

"Door Knob"
Nickname for CD 175.

Double Petticoat
An insulator with two petticoats; the outer skirt counts as one and the inner skirt counts as a second.

DP
Abbreviation for Double Petticoat, refers to an insulator with one inner skirt.

Drip Points
Small projections on the base of the insulator believed to help water "drip" off the insulator. There are many size and shape variations, but most can be described as "round" (hemispherical beads about the size of a BB) noted as RDP, or "sharp" (conical shaped projections about 1/8" in diameter) noted as SDP.
See also: FDP, RDP, SDP, WDP, Teats, SB

Dry Process
A porcelain manufacturing process where granulated clay particles are pressure molded into the desired shape.
See also: Wet Process

"Dry Spot Insulator"
Nickname for CD 182, U-188, and U-173 through U-175.

"Duplex"
Nickname for CD 187, CD 188, and U-81 through U-85.

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E

"Eared Jumbo"
Nickname for CD 269 and U-497.
See also: Jumbo

Ears
Projections on the top of insulator on either side of the saddle groove that help support the line wire or cable.

Eaves-trough
Feature around the outer edge of the top skirt of Fred Locke styles U-969, M-2335, M-2335A, M-2785, M-2795, M-2796 which collects and channels rain water to one or two spouts.

"Edison"
Nickname for CD 285 and U-356.

"Egg"
Nickname for CD 701.
See also: Confederate Egg

Embossed
A marking technique used on all insulators where the mold is punched or engraved, resulting in raised letters or other markings on the insulator. This method is used to mark all glass insulators and is one of several methods used to mark porcelain insulators.
See also: Incuse, Recess Embossed, Sand Blast, Under Glaze

Embossing
Refers to the raised writing that is embossed on the insulator.

Embossing Location Designator
A term used to describe the part of the insulator where the embossing is located.
See also: F-Skirt, R-Skirt, F-Crown, R-Crown, Dome

"Emmingers"
Nickname for CD 141.9.

"Etheridge"
Nickname for U-376 through U-376D.

"Exchange"
Nickname for CD 115 and other similar small, two-groove insulators, both glass and porcelain.

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F

F-Crown
Abbreviation for Front Crown when used as an embossing location designator. Written as (F-Crown) and used to indicate the embossing that follows is on the front crown.
See also: R-Crown, F-Skirt, R-Skirt, Dome

F-Skirt
Abbreviation for Front Skirt when used as an embossing location designator. Written as (F-Skirt) and used to indicate the embossing that follows is on the front skirt.
See also: R-Skirt, F-Crown, R-Crown, Dome

Fay Clamp Insulator
U-401 and U-401A patented by John Fay and made by Ohio Brass which used a metal clamp to secure the conductor in the cable groove.

FDP
Abbreviation for Flat Drip Points. Used to describe the type of base the insulator has.
See also: Drip Points, Base

Feeder Type
Insulators for supporting the large-diameter, low-voltage feeder cables to high-current loads.

Fins
The horizontal projections on some power insulators and transpositions designed to either increase the leakage distance from the line wire or to increase the separation between two wires that were independent but attached to the same insulator.

Fireplug
Any of three sizes of porcelain insulator with a tie-knob on opposite sides near the top, a tie-knob on top, a flared base, and a hole vertically through the center to receive a mounting nail or lag screw. These insulators were made in the 1910's and used to tie-off telephone leads before entering a house or building. Many have markings with the name "UNIVERSAL" and numbers such as "1001", "1002", or "1003" which refers to the size of the insulator.

Firing Rest
The portion of the insulator that is in contact with the kiln floor during the porcelain firing. Generally these areas are left without glaze to avoid the insulator being welded to the kiln floor.
See also: Top Rest, Teat Rest, Skirt Rest

"Fisher"
Nickname for CD 265.

Flashed Amber
A coating applied to the surface of the insulator while it is still hot. It generally results in a brown amber color. This often results in giving the appearance of streaks on the insulator. This treatment was most often used by Hemingray, such as on CD 162.
See also: Carnival Glass

"Fluid Insulator"
Nickname for CD 180.5.

"Fog Bell"
Nickname for U-418 through U-421.
See also: Fog Bowl, Fog Insulator

"Fog Bowl"
Nickname for U-846 through U-861. These unique styles were designed to limit contamination under the insulator's skirt.
See also: Fog Bell, Fog Insulator

Fog Insulator
Broad term for any insulator designed to cope with contamination problems such as fog bells, fog bowls, fog types, etc.

"Foree Bain"
Nickname for CD 144.

Forestry Insulator
Refers to several styles of small donut-shaped porcelain insulators used to suspend telegraph lines through a forest to a fire lookout tower. Most styles are composed of two halves with a large hole in the center. The overall shape of this insulator can be hexagonal, round, or oval.

"Frogs Eyes"
Nickname for CD 230.

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G

"Garity"
Nickname for CD 1040. This is a non-pintype insulator.

GB
Abbreviation for Grooved Base. Used to describe the type of base the insulator has.
See also: Base

GDB
Abbreviation for Glass Dots on Base. Used to describe the type of base the insulator has.
See also: Base

Ghost Embossing
Faint embossing that may appear on the insulator due to initial contact of the glass with the mold before the insulator is fully formed. Often the ghost embossing is near the regular embossing, but there are cases where phrases from the skirt are ghost embossed on the dome.
See also: Blotted Out Embossing

GIFONA
Abbreviation for Glass Insulators From Outside North America. For more information about this insulator book, see the Glass Insulators From Outside North America listing.

Glaze
Glaze is the thin glass coating on porcelain insulators. Glaze not only provides the great variety of colors in porcelain, but also protects the insulator surface from dirt and water.

Glaze-filled
Fusing process patented by John Boch similar to glaze-welding. Glaze-filling is different in that extra glaze is poured between the inverted porcelain shells and fired in that position so that the extra glaze flows down and fills all of the gaps between the porcelain shells.

Glaze-weld
A porcelain manufacturing technique where two or more shells of porcelain are glazed and fired together allowing the glaze to fuse the parts as a single unit.

"Grand Canyon"
Nickname for one particular shape of unembossed CD 145.
See also: Beehive

"Gregory"
Nickname for CD 159.

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H

"Haystack"
Nickname for U-166 through U-172.

"Helical"
Nickname for U-819.
See also: Spiral

"Hi-Top"
Nickname for U-782 through U-805.

"Hog Liver"
Nickname for a link strain insulator made by Ohio Brass. It is also referred to as "Pork Liver". The name refers to its odd shape.

"Hoopskirt"
Nickname for CD 152.

Horns
A shape with a curved back and circular similar to a ram's horn.
See also: Ramshorn

"Hot Cross Bun"
Nickname for CD 141.
See also: Top Groove Hot Cross Bun

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I

"Ice Cream Cone"
Nickname for CD 160.7.

Incuse
A marking technique used on porcelain insulators where the insulator is struck with a metal stamp while the porcelain is still in a plastic state before glazing or firing. This is by far the most common porcelain marking technique. The marking is actually recessed into the insulator.
See also: Embossed, Recess Embossed, Sand Blast, Under Glaze

Inner Shell
This is the bottom section of a multipart Insulator. This is the section that is usually threaded for a pin.
See also: Top Shell, Intermediate Shell

Inner Skirt
A skirt inside the insulator, often called a petticoat.

Intermediate Shell
This refers to the center section of a three part multipart or the two middle sections of a four part multipart. These can also be referred to as Top, second, third and bottom.
See also: Top Shell, Inner Shell

ISC
Abbreviation for Inner Skirt Chip.
See also: Inner Skirt

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J

JD-Blue
A distinctive light blue glaze used on Jeffery-Dewitt insulators.

"Johnson & Watson"
Nickname for CD 109.7.

"Jumbo"
Nickname for CD 140.
See also: Eared Jumbo

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K

"Keg"
Nickname for several styles, including CD 112, CD 113 and sometimes CD 114.

Kitsulator
An insulator repaired by cementing good pieces from one or more broken insulators to form one whole insulator. Note that these should be marked as repaired if they are sold.

Knob
Small cylindrical insulator used to secure house wiring or the cylindrical member projecting out from the insulator body for tying the line wire.

KPP
Abbreviation for Kerr Packaging Products.

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L

"Lily Shell"
Nickname for the beautiful flared shape of the skirts on some early multiparts which are similar in shape to a lily flower.

Line Wire
The main wire that the insulator is designed to support. The line wire is attached to the insulator with a tie wire and generally rests in the saddle groove or wire groove of the insulator.

Link Strain Insulator
This serves the same purpose as the strain insulator except it is designed to allow linking of additional insulators (similar to suspension disks) for protection at higher voltages were it is desired to insulate horizontal spans or dead-ending of feeder wires. The link strain insulator is commonly referred to as "hog liver" or "pork liver" because of its odd shape.

"Liquid Insulator"
Nickname for CD 180.

"Locke Cross Top"
Nickname for CD 204.

"Loop"
Nickname for unipart porcelain insulators U-396 to U-400B.

LRB
Abbreviation for Lightning Rod Ball. For more information about them take a look at our Lightning Rod Balls page.
See also: LRI

LRI
Abbreviation for Lightning Rod Insulator. Read more about them and view some great photographs on our Lightning Rod Insulators page.
See also: LRB

LRO
Abbreviation for Lightning Rod Ornament.

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M

M
Abbreviation for Mint. Used to describe the condition of an insulator.
See also: NM, VNM, VVNM

M-number
A M number is used to identify different shapes of multipart porcelain insulators, regardless of manufacturer or style number. An example of this notation is "M-2140".
See also: CD number, U-number

"Mad Hatter"
Nickname for CD 134.6. May also be referred to as the "Philadelphia Mad Hatter".

"Manhattan"
Nickname for CD 256.

"Mershon"
Nickname for CD 288 or U-945. The glass version may have either one or three ridges, and the latter is referred to as the "Three Ridge Mershon". The porcelain version is very rare.

"Mickey Mouse"
Nickname for CD 257 and U-395.
See also: Minnie Mouse

"Miller Twin Pin"
Nickname for CD 138.9. May also be referred to as the "Twin Pin". It was named after the original owners of the piece, Stewart and Isabelle Miller.

"Mine Insulator"
Nickname for CD 185 and U-97 through U-100.

"Minnie Mouse"
Nickname for U-393A.
See also: Mickey Mouse

MLOB
Abbreviation for Mold Line Over the Base. This is when the mold line comes down the skirt and crosses over the base to the inside of the outer skirt.
See also: MLOD

MLOD
Abbreviation for Mold Line Over the Dome. Early insulators were made with only a two piece mold, and this produced a mold line that ran over the top of the dome.
See also: Button Mold, MLOB

Mold Line
A small raised ridge on the glass, created where the seams of the mold fitted together. Typically, the mold line runs around the base, vertically up on both sides of the skirt, and around the upper wire ridge. This is the common configuration of a three piece mold.
See also: Button Mold, MLOD

"Montana"
Nickname for CD 248 along with two CD 311 sleeves.
See also: Stacker

Mud
A somewhat derogatory term that glass insulator collectors use to refer to porcelain insulators.

Multipart
An insulator made up of two or more separately glazed and fired pieces that are then cemented together. This is typically done to increase the voltage the insulator can carry.
See also: Unipart

"Muncie"
Nickname for CD 303. May also be used to refer to the smaller 7" CD 302.

"Mushroom"
Nickname for CD 176.
See also: Toadstool

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N

Nail-knobs
Refers to various porcelain house wiring insulators shaped like a cylinder with a separate cap to clamp a single wire. A nail was inserted in a hole in the center of the insulator to secure it to a rafter or wall.

NDP
Abbreviation for No Drip Points. Used to describe the type of base the insulator has. A historical term; the preferred notation for this is SB.
See also: Base, RDP, SDP

NE
Abbreviation for No Embossing. Used to indicate that there is no embossing at all on the insulator.
See also: NN

NM
Abbreviation for Near Mint. Used to describe the condition of an insulator.
See also: VNM, VVNM, M

NN
Abbreviation for No Name. Used to indicate that there is no manufacturer marking on the insulator.
See also: NE

"No Leak"
Nickname for CD 211.

"Nut"
Nickname for CD 186.2.

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O

"O'Brien"
Nickname for CD 119.

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P

Patent-top
Any of various insulator styles which have a specially designed top to eliminate the need for a tie wire. Also "self-tying", "slot-top", and "tieless". Examples are CD 109.5, CD 109.7, U-181, U-183, U-184, U-185, U-186, and U-187.

"Peacock Mickey"
Nickname for CD 257 in Electric Blue. This name started early in the hobby, and has stuck, even though the insulator is not Peacock Blue.
See also: Mickey Mouse

Pennycuick
This term is used to describe insulators produced with James Pennycuick's patent. These insulators has several unique characteristics. They have very sharp angular threads and a pointed projection in the center of the top of the pinhole. They are often crude and heavy, unmarked, and generally are light blue-aqua in color. They are found in a number of CDs such as 102, 104, 112, 121, 126, 127, 133, 134, 138.2, 145, 146.4, 149, 170 and 170.1. Note that "Pennycuick" is sometimes incorrectly spelled "Pennyquick"

Pennyquick New 8/25/13
This is a common misspelling for "Pennycuick"

Petticoat
Used to describe all skirts of an insulator, as in double petticoat.

Petticoat Rest
Unglazed surface on the bottom of the extended petticoat used for a firing rest. If the rest was glazed it would be fused to the kiln tray.
See also: Top Rest, Teat Rest, Skirt Rest

"Pilgrim Hat"
Nickname for CD 160.6.

Pin
A round piece of wood with one end that is designed to fit in the pinhole of an insulator and the other end designed to fit in a hole in a crossarm. Early wood pins were made out of oak or locust, and later pins were made of wood/metal or all metal components.
See also: Bracket

"Pin-Post"
Nickname for U-425, U-425A, and U-425B.

Pinhole
A vertical hole running through the middle of the insulator. It may or may not extend all the way through the insulator and may or may not be threaded. Designed to receive a pin or bracket.
See also: Threaded Insulator, Threadless Insulator

Plastic State
The condition of wet process porcelain after the piece is initially molded but before it has completely dried.

"Pluto"
Nickname for CD 181.

"Pogo"
Nickname for U-582 through U-593.

"Pomona"
Nickname for CD 244.

"Pony"
Nickname for a number of smaller styles of insulators. These styles include CD 102, CD 106 and others.

"Pork Liver"
Nickname for a link strain insulator made by Ohio Brass. It is also referred to as "Hog Liver". The name refers to its odd shape.

Power Insulator
An insulator designed for carrying greater electrical power. The line wire on most power insulators rests in the saddle groove. Some power insulators used a separate sleeve for additional insulating qualities.

PR
Abbreviation for Petticoat Rest. Refers to location of the firing rest.
See also: SR

"Provo"
Nickname for several styles, including "0 Provo" CD 249, "1 Provo" CD 283, "2 Provo" CD 282 and "4 Provo" CD 303.5.

"Purkey"
Nickname for U-186.

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R

R-Crown
Abbreviation for Rear Crown when used as an embossing location designator. Written as (R-Crown) and used to indicate the embossing that follows is on the rear crown.
See also: F-Crown, F-Skirt, R-Skirt, Dome

R-Skirt
Abbreviation for Rear Skirt when used as an embossing location designator. Written as (R-Skirt) and used to indicate the embossing that follows is on the rear skirt.
See also: F-Skirt, F-Crown, R-Crown, Dome

Radio Treatment
This term refers to special conductive glazes used in the wire groove or saddle groove as well as the pin hole to reduce AM radio interference. This treatment often produces very striking color combinations.

"Ram's Head"
Nickname for CD 109.9. Similar to the Claw.

Ramshorn
An iron rod with one end inserted in the insulator (either rubber, composition, or metal-clad glass) and the other end shaped like a ram's horn. The conductor is secured to the insulator by threading it through the opposing "horns".

"Ranson"
Nickname for U-183.

RB
Abbreviation for Rounded Base. Used to describe the type of base the insulator has.
See also: Base

RDP
Abbreviation for Round Drip Points. Used to describe the type of base the insulator has. Round Drip Points are hemispherical beads about the size of a BB on the base.
See also: SDP, Drip Points, Base

Recess Embossed
A marking technique used on porcelain insulators similar to incuse marking where the insulator is struck with a stamp that indents an entire area while leaving a raised marking, as opposed to the indented incuse marking.
See also: Embossed, Incuse, Sand Blast, Under Glaze

"Redlands Insulator"
Nickname for a triple petticoat insulator design made famous in the late 1890's when used on a power line in Redlands, CA. These insulators are U-746 and U-935.

RFI
Abbreviation for Radio Frequency Interference.

"Roman Helmet"
Nickname for several styles, including CD 258, CD 259, CD 260, and U-377 through U-389.

RR
Abbreviation for Rainbow Riders (Trading Post). For more information about this insulator magazine, see the Rainbow Riders Trading Post listing.
See also: CIC, CJ

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S

Saddle Groove
A top wire groove used to hold the line wire.

Sand Blast
A marking technique used on porcelain insulators where the finished insulator is held against the contoured head of a sandblast machine. This resulted in the marking being dull compared to the glossy glaze around it.
See also: Embossed, Incuse, Recess Embossed, Under Glaze

Sand Glaze Rest
An unusual firing rest technique that uses very coarse sand to minimize contact of the insulator and the kiln.
See also: Top Rest, Skirt Rest

"Santa Ana"
Nickname for CD 178.

SB
Abbreviation for Smooth Base. Used to describe the type of base the insulator has. A Smooth Base is flat to slightly rounded.
See also: Drip Points, Base, CB

SCA
Abbreviation for Sun Colored Amethyst; a light purple color. Glass containing small amounts of manganese when exposed to ultraviolet rays (i.e. the sun) over time will turn a light purple color. Today the term is not used to describe a light purple color because it is often unknown if the purple color originated from the presence of manganese.

Screw-top
Various patented insulator styles with a coarse external thread-like spiral groove formed on the top of the insulator (with a twist opposite to that in the threaded pinhole) for the purpose of replacing broken insulators without replacing the tie wire. While the insulator was screwed down on the pin, the existing tie-wire loop could be simultaneously secured to the top of the insulator by placing it in the reverse twisting external spiral groove where it would travel down to the tie-wire groove. Various styles include CD 110, CD 110.5, CD 110.6, CD 147, CD 150, U-2021.
See also: Spiral Groove

"Screw-Top Boston"
Nickname for CD 158.9.

SDP
Abbreviation for Sharp Drip Points. Used to describe the type of base the insulator has. Sharp Drip Points are conical shaped projections about 1/8" in diameter on the base.
See also: RDP, Drip Points, Base

"Seilers"
Nickname for CD 130.2.

Shell
One part of a multipart glass or porcelain insulator. Multiple shells are cemented together to form one multipart insulator. Also may describe the bowl-like porcelain parts that were nested and fused together with glaze to make the glaze-welded and glaze-filled unipart porcelain insulators.

"Signal"
Nickname for CD 162 and other similar distribution styles, both glass and porcelain.
See also: Baby Signal

Sim
Abbreviation for "similar". Used with U-numbers (Sim U-860) to describe an insulator that matches that style closer than any other in the U-Chart. If significantly different, the description might note the character of the difference, for example, "Sim U-860, crown as U-850".

Skirt
The outer part of the insulator, from the wire ridge to the base. Also used to refer to all skirts, including the inner skirts.
See also: Inner Skirt, Petticoat

Skirt Rest
A firing rest on the base of the insulator skirt. The firing area is usually unglazed.
See also: Top Rest, Teat Rest

Sky Glaze
Sky glaze is the standard light blue-gray color of modern insulators. This should not be confused with earlier light blue or mottled gray insulators.

"Slash Top"
Nickname for CD 788 and U-988.

Sleeve
A separate piece of glass or porcelain that is used to cover the pin to increase the electrical resistance on some power insulators.

"Slice, The"
Nickname for CD 148.

"Slim Pin"
Nickname for one particular style of non-pintype insulator. This insulator falls outside of the CD numbering system.

Slot-top
Any of various insulator styles which have a specially designed top to eliminate the need for a tie wire by mean of a slot to receive the line wire. It may also be referred to as "self-tying", "patent-top", and "tieless". Examples are CD 141.7, CD 141.8, U-183, U-185, and U-186.

Slug Embossed
A raised band of glass on which the embossing appears, like that of a "Slug Plate" familiar to many bottle collectors.

"Snow Cone"
Nickname for CD 160.7.

"Spaceman"
Nickname for CD 181.5.

"Spiral"
Nickname for U-820.
See also: Helical

"Spiral Groove"
Nickname for CD 110, CD 147 and CD 150.
See also: Barclay

Spooks
Small white porcelain insulators used to support neon tubes. Small holes in the insulator were used to thread tie wires through to secure the neon tube.

Spout
A feature on the outer edge of porcelain eaves-trough style Fred Locke insulators which directs rain water away from the insulator and crossarm.

SR
Abbreviation for Skirt Rest. Refers to location of the firing rest.
See also: PR

"Stacker"
Nickname for CD 248 along with two CD 311 sleeves.
See also: Montana

Standard Porcelain
Refers to several dozen standard styles of porcelain knobs used for house and industrial low voltage surface wiring. Most have a smooth hole through the insulator so it could be secured with a screw, nail, or bolt.

"Stovepipe"
Nickname for U-180, U-180A, and U-180B.

"Straight Sides"
Nickname for CD 267.5.

Strain Insulator
An insulator used to break the electrical path in any wire link, such as in guy wires used to support utility poles, dead-ending the ends of electrical power lines, or ends of radio antenna wires. Note that the interlocking connecting wires on all strain insulators (except radio antenna strains) prevent the wire from falling should the insulator become broken. Several older styles of a high voltage strain insulator intended to dead-end feeder wires were mounted vertically between two crossarms by means of a wooden or metal rod or pipe. The larger styles were composed of a smaller porcelain part cemented inside the larger diameter porcelain sleeve.
See also: Link Strain Insulator

Style Number
A number used by an insulator manufacturer to identify different types or styles of insulators that they produced. In some cases, different manufacturers would use the same style number to designate a specific insulator, while in other cases the style number would be different. An example of this notation is "HEMINGRAY-42".
See also: CD number, M-number, U-number

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T

"Teapot"
Nickname for CD 790 and U-990.
See also: Baby Teapot

"Teardrop Pony"
Nickname for CD 109. May also be referred to as the "Chicago Teardrop Pony".

Teat Rest
A firing rest on the base of the insulator skirt. The firing area is usually unglazed. A firing rest developed by Ohio Brass composed of four small raised teats on the crown. When the insulator was glazed all over and fired upside-down, the insulator was broken off the firing surface, leaving four small white spots on the crown.
See also: Skirt Rest, Top Rest

Teats
A word used in the early 1900's to describe Drip Points. Hemingray Glass Company ads for insulators often included the phrase "See the teats on the petticoat".

"Teepee"
Nickname for CD 157.

Thimble
A threaded metallic insert cemented or molded into the pinhole.
See also: Brass Bushing

Threaded Insulator
An insulator whose pinhole is threaded to fit a corresponding threaded pin.
See also: Threadless Insulator

Threadless Insulator
An insulator whose pinhole has no threads.
See also: Threaded Insulator

"Three Rumple"
Nickname for CD 116.

"Tick"
Nickname for M-3900.(The Tick).

Tie Wire
The wire used to securely attach the line wire to the insulator.
See also: Tie Wire Groove

Tie Wire Groove
Groove in the side of the insulator used to secure the conductor by wrapping a short length of wire around the insulator and the line wire.
See also: Tie Wire

Tie-knob
The end of a cylindrical insulator (such as a Universal fireplug) with a tie wire groove used to attach a line wire.

"Toadstool"
Nickname for CD 176.9.
See also: Mushroom

"Toll"
Nickname for CD 121; sometimes also used to refer to CD 122, as well as U-106 through U-110.

"Top Groove Hot Cross Bun"
Nickname for CD 208.
See also: Hot Cross Bun

Top Rest
A firing rest on the top of the insulator. These insulators will generally have no glaze on their top surface.
See also: Teat Rest, Skirt Rest

Top Shell
The top portion of a multipart insulator.
See also: Inner Shell, Intermediate Shell

"Tramp"
Nickname for Transposition style insulators CD 190 to CD 205 such as CD 196 and U-191 to U-225.
See also: Transposition

Transmission
The high voltage power lines between the power generating source and the lower voltage primary distribution networks.

Transposition
An insulator specially designed to accommodate two separate line wires and be able to "transpose" or swap them. The wire that started on the left would end up on the right and visa verse. This was required to reduce the crosstalk that resulted when wires were run parallel to each other.

TS
Marking on CD 129. The "TS" stands for transposition intended to be used on a steel pin. These insulators were used on telephone lines.
See also: TW

TS 2
Marking on CD 142. The "TS" stands for treated side groove. These insulators were used by Western Union on telegraph lines.
See also: TS 3

TS 3
Marking on CD 142.4. The "TS" stands for treated side groove. These insulators were used by Western Union on telegraph lines.
See also: TS 2

TW
Marking on CD 203. The "T" stands for Transposition insulator and the "W" denotes the insulator was intended to be used on a Wooden pin. These insulators were used on telephone lines.
See also: TS, CW

"Twiggs"
Nickname for CD 141.7.

"Twin Pin"
Nickname for CD 138.9. May also be referred to as the "Miller Twin Pin".

"Two Spout"
Nickname for M-2335.

"Two-piece Tramp"
Nickname for transposition insulators composed of two separate parts such as CD 190/191, CD 192/193, CD 194/195, CD 194.5/195.5 and U-220 to U-225.

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U

U-number
A U number is used to identify different shapes of unipart porcelain insulators, regardless of manufacturer or style number. An example of this notation is "U-123".
See also: CD number, M-number

Under Glaze
A marking technique used on porcelain insulators where an ink stamp is used on the dry porcelain prior to glazing, and then shows through the transparent glaze after firing.
See also: Embossed, Incuse, Recess Embossed, Sand Blast

Unipart
A porcelain pin-type insulator that is fired as a single piece. This does include glaze-weld pieces.
See also: Multipart

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V

"Viking Helmet"
Nickname for CD 307 and CD 308.

VNM
Abbreviation for Very Near Mint. Used to describe the condition of an insulator.
See also: NM, VVNM, M

VVNM
Abbreviation for Very Very Near Mint. Used to describe the condition of an insulator.
See also: NM, VNM, M

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W

"Wade"
Nickname for the "Dot-Dash Wade" CD 723 and the "Smooth Wade" CD 723.3.
See also: Baby Wade

"Washboard"
Nickname for CD 739.5.

WDP
Abbreviation for Wedge Drip Points. Used to describe the type of base the insulator has.
See also: Drip Points, Base

Wet Process
A porcelain manufacturing process where the insulator is formed from clay in the plastic state. This process generally provides much higher quality insulators by greatly reducing the air trapped in the clay.
See also: Dry Process

Whittle Mold
Used to describe the surface erosion of a mold that creates almost a leathery or reptile scale look to the surface of the glass. This term is usually used by bottle collectors who refer to old bottles blown into wooden molds. Some Canadian CD 143's have this 'whittle mold' characteristic.

"Wing Chambers"
Nickname for CD 124.5. Used in conjunction with the Bell Chambers CD 317.5.
See also: Chambers Companion, Candlestick

Wire Groove
The square or concave section between the wire ridges on the side of the insulator that holds the line wire.
See also: Saddle Groove

Wire Ridge
A ring of glass around the insulator above and below the wire groove designed to help support the line wire and the tie wire.

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Last updated Tuesday, April 18, 2000