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A History of
New England Insulators

by Joe Maurath, Jr.View Icon Profile

This article contains updated summarized research information not included in "A History and Guide to North American Glass Pintype Insulators" (1990) describing each New England insulator style, special order user name and manufacturer.

The Beginning: Threadless Insulators

Soon after the invention of the telegraph in 1844, commercial lines were being built by telegraph companies springing up all over the country. This construction prompted the necessity for a great many insulators to support the increasing thousands of miles of wire being strung each year. The earliest insulators were produced by companies who had already been marketing other wares. Most of these firms offered telegraph and lightning rod insulators as a sideline item. A description of these manufacturers and what is known about their insulators follows.

New England Glass Company

Incorporated in 1818, this organization was based in Cambridge, Massachusetts (a Boston suburb) and was known for its high-quality glassware. Historical research yields some evidence that the earliest pintype glass insulators were made by this company for Ezra Cornell. Mr. Cornell was an early telegraph entrepreneur who conceived the glass "bureau knob" design in 1844. From 1846 to 1850, many insulators were made by Boston area glassmakers for the telegraph line construction overseen by Mr. Cornell. Among these glassworks, it is known that the New England Glass Company made insulators for his ventures, beginning some time during 1847 or 1848. By 1850, Mr. Cornell owed New England Glass Company the large sum of $1,200. His unpaid balance resulted in the termination of insulator shipments. It is not known what, if any, insulator manufacture took place at the New England Glass Company after that time.

Boston and Sandwich Glass Company

This glassworks operated on Cape Cod in Sandwich, Massachusetts, commencing around 1825. Like the New England Glass Company, this firm also was known for their high quality tableware and ornamental glass. Production continued until the plant closed in the late 1880's. Insulators were not a significant item; however, a number of CD 701, CD 701.1, and possibly CD 724 threadless and lightning rod insulators attributable to this works have been located. Although the threadless specimens made there date between the 1850's and mid 1860's, lightning rod insulator production continued until much later.

Other Early Manufacturers and Types of Insulators

New Granite Glass Works

This glassworks, organized in 1861, was among the suppliers of telegraph insulators in New England during telegraph's early days. Mr. George Foster managed the operations of the plant, which stood in Stoddard, New Hampshire. There is evidence that telegraph and lightning rod insulators were offered by the firm. None have been located with lettering; however, it is speculated that a considerable number of insulators were made there. The works remained until 1871, when it was destroyed by fire. Four other glass companies were established in the Stoddard, New Hampshire area from 1842 through 1861. It is entirely possible that some of these made insulators, although the New Granite Glass Works is the only one that is known to have offered them.

Thames Glass Works Company

This organization, located in New London, Connecticut, made a brief stand between 1863 and 1865. The company was known as a manufacturer of light and dark green glass. Although no advertising or other printed information presently exists that mentions they made insulators, an incomplete specimen attributed to this glassworks has been located. This item consists of a CD 718, CD 731 or similar style's upper half in deep amber glass lettered THAMES GLASS WORKS - NEW LONDON around the lower portion of the crown.


It was not long after the first glass threadless pintype insulators were made when pottery companies thought about producing telegraph insulators. A well-known pottery at Bennington, Vermont had been quite successful producing other wares, and during the early 1850's they began production of telegraph insulators. Numerous styles were made and some became rather popular. An early telegraph line between Boston and New York City was outfitted with many of Bennington's "white flint" insulators. These insulators received excellent reviews because of their superior insulating qualities. Most Bennington threadless are white. Other colors, particularly those that are grayish or mottled brown, are extremely rare.

Unique New England Early Telegraph Designs

A couple of interesting telegraph insulators are on exhibit along with the porcelain and glass pintypes. The first of these are the "ramshorn" hook insulators which were used in substantial quantities on a line to the top of Mount Washington in New Hampshire. Not much is known about who made these; however, many collectors agree that the glass inserts within the ramshorns' bodies were made by at least one of the five glassworks that existed in Stoddard, New Hampshire.

An odd threadless design apparently made of iron, nicknamed the "Wolfman," was discovered in Maine during 1994. The insulator was located along an old railway right-of-way and there are no clues at present that explain its peculiar design.

Massachusetts Glass Company

Formed during May 1867, this works existed in Somerville, Massachusetts. Samuel Oakman was president. The company continued under this name until 1871, when the property transferred ownership. After that time, the Boston Bottle Works was listed at the same address as the Massachusetts Glass Company, and Samuel Oakman continued in charge of the operation there.

Most likely, the first insulators produced by Mr. Oakman were unthreaded, with "slotted" pinholes. On July 26, 1870, he was granted a patent for this concept of securing insulators to their mounting pins. These insulators are readily identified by an elongated, indented area along each side of the pinhole cavity. When the insulator was pressed down upon a special wooden pin, the expansion of the pin's upper section provided the necessary grip to prevent the insulator from unfastening or loosening. Apparently this idea was conceived as an improvement beyond threadless insulators; however, there were a couple of drawbacks. Special pins were required for Oakman's slotted threadless insulators. It was also likely that many eventually shook loose from their pins due to line vibration, expansion and contraction of the wire, etc. For these reasons, the insulators never became popular and were a short-lived design.

Slotted threadless insulators are known in three styles and some are marked only with Oakman's 1870 patent date. These were probably made at the Massachusetts Glass Co. plant, and later specimens were most likely produced at the Boston Bottle Works facility.

Early New England Threaded Insulators

Boston Bottle Works

From 1872 to 1877 Samuel Oakman was listed as agent for this organization. No doubt he played a significant role in overseeing glassmaking there. At present the remaining company officers have not been identified.

Among the many glassmaking and insulator patents issued to Mr. Oakman from 1869 to 1904 is his segmented threading concept, patented on October 15, 1872. His idea allowed the threading plunger to be withdrawn from the insulator's newly formed pinhole cavity without unscrewing it. Instead, the special threading mandrel only had to be twisted a portion of a turn and then removed. Titled "Improvements in Formers for Segmentally Screw Threaded Insulators," two separate patents were issued to Mr. Oakman on that date. Each provided simplified and less expensive insulator manufacture. One patent resulted in insulators with three-segment threads; the other in four-segment threads. Comparable quantities of Boston Bottle Works insulators with each threading characteristic have been located. Since there was a reduction of contact between the insulator and pin, it is possible that insulators with segmented threads did not hold securely over a period of time. This eventual drawback probably led Mr. Oakman to his first full threading patent, issued to him on September 13, 1881. It is rather obvious that Samuel Oakman was rather concerned about reducing insulator production costs throughout his career. His glassmaking patents through the years certainly reflect this, providing an interesting variety of insulator designs and pinhole varieties.

Also characterizing Oakman's insulators is lettering around their bases, as opposed to on the insulators' skirts or crowns. Almost all Boston Bottle Works insulators are embossed in this unusual manner.

Unlike other insulators produced by Samuel Oakman during his glassmaking career (which lasted until 1897), specimens made at the Boston Bottle Works are diverse with color. Although the majority are aqua, others have been located in many shades of green, ranging from very light to deep emerald. Others are of dark amber hues, from olive to root beer amber. Many of these scarcer colors appear in the displays.

Boston Bottle Works insulators are not of contemporary design, as you will note in the exhibits. Rather, they are of peculiar shapes. Most interesting and eye-catching is the screw-top variety (CD 158.9). No patent information has been uncovered regarding this style. It seems logical that a screw-threaded cap with an indented wire groove protruding through the center of the cap provided a method of attaching the line to the insulator without a tie-wire. It is likely that eventual breakage of such wooden or glass caps dropped the line wire, leading to the rapid demise of the CD 158.9 design.

Also unique to Boston Bottle Works manufacture are their many insulators with hexagonal, six-sided crowns. This feature probably enabled the lineman to better grip the insulator while securing it to the mounting pin.

Bay State Glass Works

After the Boston Bottle Works closed its doors in 1877, the Bay State Glass Works was formed. Samuel Oakman was listed as agent while the company was in business through early 1879. Their salesroom was at 97 State Street, Boston, as was that of the Boston Bottle Works. The company's factory was at 223 Bridge Street, Cambridge. It is unclear what became of the former Boston Bottle Works in Somerville.

Although insulators were not advertised by the Bay State Glass Works, it is probable that some were made there. Specimens most likely attributable to this works are styles identical to Boston Bottle Works insulators and are either without markings or lettered only with Oakman's 1872 patent date.

Oakman's Insulators: 1880-1883

After the Bay State Glass Works plant closed in 1879, Mr. Oakman continued pursuing his glassmaking career. He spent the following years at various glassworks before becoming associated with the American Insulator Company around 1883. His activities during this period are difficult to trace.

During 1880 Samuel Oakman was simply listed in the Boston City Directory as "treasurer for glass company." It remains unknown what organization he was affiliated with at that time.

On September 13, 1881, Mr. Oakman was issued a full-threading patent, which was also assigned to Edward Sherburne. Mr. Sherburne operated a window and plate glass factory in Boston. Evidently Samuel Oakman had been working for Mr. Sherburne at the time. Although no insulators positively traceable to the Sherburne works have been located, a solitary CD 134 specimen in purple glass lettered only with Oakman's 1881 patent date may have originated there. Quite possibly Samuel Oakman produced a few insulators of his own after hours at the Sherburne glassworks as prototypes of his 1881 threading process. Using leftover window glass would have produced the above purple CD 134 insulator, the only known specimen in purple glass attributable to his manufacture. Other insulators possibly made by Oakman during his stand at the Sherburne Glass Company are CD 134 insulators lettered only with his 1881 patent in aqua, and identically embossed ones that also have OAKMAN appearing around their base rims. All of these are rare.

American Insulator Company

Office listings for this organization took place between 1884 and 1886. During 1884 the company was located on Temple Court in New York City and at an unidentified location in Boston. D.J. Hearn was the firm's general agent in Boston up until April 1884. A month later he became general manager at American's New York City address and Mr. H.C. Andrews was the company's treasurer. No mention was made about Samuel Oakman until a year later. Mr. Oakman appeared during 1885-1886 when both he and the American Insulator Company had city directory listings at 2 Wall Street, New York City. It seems most probable that the Boston and New York City references to the American Insulator Company referred to the same firm. The origin of the company's insulators has not been positively identified.

The earliest American Insulator Company specimens most likely were produced during 1883 or a bit earlier. Because of their base embossing, Samuel Oakman undoubtedly played some part in the manufacture of all American Insulator Company varieties. Furthermore, it is speculated the later American insulators (easily identified by their small, fine base lettering as found on their CD 145 "beehive" style) were produced at the American Iron Glass Pipe and Plate Company in Haverhill, Massachusetts during 1885. No clues exist where earlier (circa 1883 - late 1884) American Insulator Company specimens were made. These have larger base lettering accompanied by Oakman's 1881 patent date as seen on CD 134 American insulators.

The majority of American Insulator Company insulators are aqua, light greenish or light blue. Although uncommon, others are in attractive colors such as yellow-green, olive amber, emerald green and olive-green shades. Examples of these desirable colors are included with the displays.

Insulators produced by this company are mostly of the standard smaller styles used during the 1880's. Most common is the CD 145 which became the Western Union Standard shortly after Oakman's 1884 design patent of this style was granted. Also of significance was his November 13, 1883 patent regarding his "inner skirt" concept, which the CD 145 and many other glass insulator styles employed thereafter.

Unusual American Insulator Company designs are the CD 105, CD 156, CD 156.1 and CD 160.7. These are unique to American manufacture. Most styles were widely distributed throughout the United States, and the more common ones evidently were made in large quantities.

National Insulator Company

Office listings for this company are in Boston and New York City for the year 1886 and during 1885 as the National Glass Screw Company.

Associated with their manufacture was Lawrence B. Gray, a moldmaker who resided in Boston during the 1880's. He was issued several insulator and insulator manufacturing patents during that time.

Evidence exists that some, and probably all, National insulators were produced at the American Iron Glass Pipe and Plate Company (abbreviated as the "Iron Glass Company") in Haverhill, Massachusetts. This organization began during mid-December 1884 and continued for the following five months. Newspaper accounts of the day stated "when the factory is in full running order its capacity will be equal to the production of 15,000 insulators per day, employing 50 or so workmen."

Even if this glassworks got up to only partially full production, an incredible number of insulators were made there during its brief stand. It was also stated within a newspaper article during January 1885 that the Iron Glass Company was producing insulators for undisclosed companies who held valuable patents. It is quite probable that the works made insulators with the American Insulator Company name and for other organizations as well. All four National styles are uncommon, so it stands to reason that other insulator companies also held contracts with the Iron Glass Company.

All National insulators are lettered around their bases, like American Insulator Company specimens. It is apparent that Samuel Oakman played somewhat of a role in insulator manufacture there. He had 15 years of insulator-making experience at the time, and he was employed at the Iron Glass Company overseeing bottle production in the plant.

Of the National styles, most interesting are the "corkscrew" designs (CD 110.5 and CD 110.6). Patents associated with these odd styles regarded attachment of a special horse-shoe shaped clip to readily grip the line wire to the base of the crown's spiraling threads.

Most National insulators are of aqua glass. A few light green specimens have been located and these are rare.

Oakman Manufacturing Company

This glassworks was in operation between 1890 and 1897. The factory stood on Mercer Street in South Boston, and the office was at 219 State Street. During its seven year existence, Samuel Oakman was treasurer. In 1892 the company changed to the Oakman Glass Works, although the embossing on the insulators remained the same.

As opposed to small communication and low voltage styles, the company specialized in larger, heavy power distribution designs, especially those intended for supporting heavy direct-current trolley car cables. About 1895 the first underground transit system in the United States was placed in service in Boston. A great many CD 140 "Jumbo" insulators were commissioned for this project, and many of them were produced by Oakman. Most CD 140 insulators in the hands of collectors were originally used on this pioneer line. Brookfield also provided some insulators of this style while this line was being constructed; however, these are unmarked.

While the Oakman facility was in operation in South Boston, Samuel Oakman was issued numerous patents of significance. Most notable is his "saddle groove" design, patented on June 17, 1890. This concept remains basically unchanged on insulators made today! On May 12, 1891, he was issued a patent for the "Columbia" design, which provided one or two "eyes" molded into the insulator for more adequately securing the line's tie wires. A patent granted on August 19, 1890 concerned concentric ridges spiraling around the inside of the insulator's outermost skirt, intended to accomplish better insulation.

After the Oakman works closed in 1897 there is no evidence linking Samuel Oakman with any glassmaking ventures. However, in 1904 he was issued a patent for a peculiar insulator design which has not as yet been located.

The Standard Glass Insulator Company

This organization was listed in the Boston City Directory during 1893 and 1894. Lawrence B. Gray was also listed at the company's 120 Tremont Street office location. The company advertised as "Manufacturers of Glass Insulators by Lawrence B. Gray's Patent Process." Mr. Gray was associated with the National Insulator Company (1885-1886) and was a Boston moldmaker who held numerous insulator patents. It is evident Lawrence Gray had much influence during the manufacture of Standard insulators. At the present time the location of the company's glassworks remains unknown.

All Standard insulators are quite uncommon and seven styles have been located. These are of low-voltage and communications designs. A very interesting saddle groove variant, identified as CD 268.5, is known to collectors. Bearing Lawrence B. Gray's August 8, 1893 patent date on the skirt, this saddle groove design was intended to be "pleasing to the eye."

All Standard insulators are lettered around their base rims, like those produced by Samuel Oakman. Mr. Oakman so far has not been identified as having been associated with Standard insulator manufacture.

A substantial amount of glass consistency was used in making Standard insulators. Almost all are light aqua or light blue. Light green examples in the CD 138.2 and CD 157.5 designs are known and are uncommon.

Lawrence B. Gray Patent Process Insulators

Two or three CD 138.2 insulators have been located lettered around their base rims MANUFACTURED BY LAWRENCE B. GRAY'S PATENT PROCESS. These are of unknown origin. It is possible Mr. Gray made these on his own at a location other than at the Standard Glass Insulator Company facility. Or, possibly, another glassmaker was allowed to produce these with license to Gray's patents.

Lawrence B. Gray insulators bear large lettering, similar to their Standard counterparts. Their obviously differing characteristic is the odd bluish-lavender color in which they have been found.

James Pennycuick and His Insulators

On August 11, 1885, James Pennycuick of Boston, Massachusetts was granted a patent for a "Method Of Forming Screw-Threads On Glass." No mention about insulators was made within the patent text.

During 1888 the Boston and Sandwich Glass Company closed their plant, which stood in Sandwich, Massachusetts on Cape Cod. Mr. Pennycuick purchased this property during December 1889, having recently formed the Electrical Glass Corporation. He was the company's director and was eager to get the glassworks up and running. Newspaper accounts of the day indicate that Mr. Pennycuick was very interested in manufacturing insulators, and almost immediately made prospective customers aware of his product by distributing insulator samples. Since he did not begin glassmaking until several months later, he had his samples made by the Sandwich Cooperative Glass Company. Delays in production and labor problems at Mr. Pennycuick's plant created a substantial backlog of orders for his insulators. His prospective customers liked the samples and orders continued to arrive. Obstacles he encountered at his glassworks caused him to cease operations during November 1890, only six months after glass making began. The property was foreclosed upon a short time later and sold at a public auction.

Nothing is known about the styles or lettering that concern the insulators produced at the Sandwich Cooperative Glass Company or at the Electrical Glass Corporation. At a minimum it seems obvious Mr. Pennycuick identified some with his 1885 patent date. It is noteworthy that these also bear the letter "P" within a diamond monogram boldly appearing on their skirts: . The letter P on these could represent Pennycuick; however, no proof currently exists. All appear to have been threaded by his patent process. These rare specimens have high quality, fine, concise threading that was unusual for insulators of that time.

The majority of insulators located with this noticeable, characteristic threading are unmarked and are known in many styles. Most of these are aqua. Exceptions are those in light to dark blue and green shades. Some of these are quite intense and vivid; a few have swirls and bubbles, etc. Many examples of these colorful Pennycuick-threaded insulators are shown in the accompanying displays.

Like their unmarked counterparts, Diamond-P embossed insulators appear to have been very well made. These have only been found in CD 134, and many collectors believe they are the most colorful of all Pennycuick-threaded specimens. The majority of Diamond-P's are aqua. Others have been located in many shades of blue and green. Interesting examples include those in sapphire, cornflower and teal blue. Slag, bubbles, swirls and other inconsistencies add spectacular beauty to some of these oddly colored insulators. Most Diamond-P insulators have been located in Eastern Massachusetts. All are rare, even the aqua ones.

Other CD 134 specimens with lettering and Pennycuick pinhole threads are those with C.E.L.CO. and PETTINGELL ANDREWS embossing. They are also identical to the outer shape and size of Diamond-P insulators. These corresponding features suggest the possibility that the same glassworks and/or moldmaker made all of these CD 134 insulators. Or at least that the C.E.L.Co. and Pettingell Andrews ones were manufactured by someone who had rights or access to Pennycuick's threading technique.

New England Glass Manufacturing Company

This organization was listed in the Boston City Directory only during 1899. The location of their glassworks remains unknown. A great many insulators were produced by this firm. Specimens bearing N.E.G.M.CO. bold lettering on their skirts have been located in eight styles. Many of these designs were apparently distributed widely around the country.

Of particular interest are the CD 267 and CD 267.5 styles. All of the latter and most of the former N.E.G.M.Co. insulators that have surfaced were used on an eight-mile section of elevated transit line built around 1900 in Boston. The insulators supported heavy, 1 1/4-inch diameter copper cables which were positioned at approximately twelve-foot intervals beneath the railway's catwalk. The railway and all insulators were taken down and removed during 1987 and 1988. A number of Brookfield-made CD 267 insulators marked NO. 4 CABLE and some unembossed units, all in varying shades of aqua, were also mixed in with the N.E.G.M.CO. lettered cables. Although a few have been found elsewhere, most CD 267 insulators known were used on this installation.

The CD 267.5 and smaller cable style, CD 250, are unique to the company's manufacture. N.E.G.M.Co. insulators are generally aqua, greenish or blue. Scarcest are those in olive green shades and sapphire blue.

The New England Glass Manufacturing Company is the last glass insulator company that existed in New England.

This is an interesting article about the history of the CD 267 and CD 267.5 insulators.

Special Order Communications Insulators

So. Mass. Tel. Co.

The first company to arrive on the scene in New England and order insulators with their name or initials was the Southern Massachusetts Telephone Company.

This organization began during 1878 and served numerous communities in southeastern Massachusetts and on Cape Cod. Following the early 1900's, the company gradually sold their telephone exchanges to the New England Telephone and Telegraph Company until the So. Mass. Tel. Co. was fully dissolved in 1939.

Insulators made for this company are very likely Brookfield products and are of the CD 102 "pony" design. They were produced between 1890 and 1910 or so. Most are aqua; however, a few have been found in clear or off-clear glass.

Likely commonplace on lines within their service territory in their day, these rather desirable insulators are representative of the only non-Bell telephone company who ordered such personalized insulators.

New England Tel. & Tel. Co.

Organized during 1883, this company provided telephone service to the majority of cities and towns in New England. From their beginning through the 1910's they ordered insulators with their initials appearing on them.

The earliest New Eng. Tel. & Tel. Co. insulators are CD 104, CD 112 and CD 110.5 specimens with the name appearing on the skirt. National Insulator Co. lettering appears on the base rim of the latter and on a few CD 104's. Also among the first of these insulators are a very few of the CD 102.4 design. These are simply embossed N.E.TEL.& TEL.CO. around the base. It is not known who manufactured these peculiar insulators. Most are aqua, although one or two have been found in light green glass.

The vast majority of New Eng. Tel. & Tel. Co. insulators are of Brookfield origin. Production of these specimens by this glassworks likely commenced shortly before 1890. These early Brookfields can be identified by the mold line over the crown and the swirl-start threading. Later Brookfields were made in three-part molds.

Most common is their CD 104 pony. These have been located in many aqua and green shades. The more vibrant green New England Tel. & Tel. Co. insulators are scarcer. A CD 104 specimen has been identified in purple glass and so far is the only one known to exist.

CD 121 "toll" insulators and double-groove CD 112 "kegs" also were specially made for the company, most likely by Brookfield. Those of the latter design are uncommon.

City Fire Alarm and Fall River Police Signal Insulators

No doubt of Brookfield manufacture are insulators made on special order for the city of Fall River, Massachusetts. These "personalized" insulators were used on crossarms identifying municipal fire alarm and police call box circuits.

Produced some time between 1900 and 1915, these insulators are known in the CD 133 and CD 134 styles. The latter are boldly lettered FALL RIVER POLICE SIGNAL on the skirt, while the CD 133 insulators are prominently marked CITY FIRE ALARM. All are aqua.

Most of Fall River's signal system was upgraded to modern paired cable, so just about all of their open-wire construction is now gone. All known City Fire Alarm and Fall River Police Signal insulators in collectors' hands today were once used in that city. To date none have been reported found elsewhere.

Boston Area Electrical Supply Companies

Thomson-Houston Electric Company

During 1883 this well-known, prominent electrical distributor began operation and offered a wide variety of related goods. Their headquarters was in Boston, supplemented by additional offices in major cities throughout the United States. The popularity of and requirement for their electrical distributing equipment and lighting accessories enabled the firm to grow. Insulators were specially made for Thomson-Houston until they consolidated with General Electric in 1892.

Most T-H.E.Co. insulators were produced by Brookfield, although some were made by Hemingray. Brookfield examples are more common and are known in CD 134 and CD 162. All are aqua except for the scarcer CD 134's in green. These range from light, pale shades to deep olive. In addition, a very few Brookfield-made T-H.E.'s are known in deep root beer amber. These were probably made by using leftover glass intended for producing a run of beer bottles. Most deep amber T-H.E.Co. specimens originated from two or three municipal fire alarm systems in southeastern Massachusetts. All are indeed rare.

Hemingray made T-H.E.Co. insulators only in the CD 134 style. These are unusually lettered, with the company's initials appearing across the very top of the insulator's crown. These are usually light greenish and bear the Hemingray 1871 patent date on the skirt.

Probably of Brookfield origin are some odd T-H.E. specimens of the CD 143.5 style. These aqua insulators are lettered T-H.E.CO. across the upper portion of the crown and have Brookfield-like swirl-start threading. No information exists at this time that explains their out-of-the-ordinary design. These have been seldom found. Also attributed to Thomson-Houston are a few CD 245 specimens lettered T-H in bold letters on the skirt, with 9200 appearing on the reverse side. These are probably Brookfields, also.

General Electric Company

This well-known company was formed in 1892 as a result of the consolidation of Edison General Electric, Thomson-Houston and several other larger companies.

The earliest insulators specially manufactured for General Electric are Brookfield products. These were made in former T-H.E.Co. molds. Evidence of this is "ghosting" of the letters T-H. replaced by the letter G. It seems likely these aqua or greenish CD 134 insulators were produced through the mid or later 1890's.

Successive G.E.Co. marked insulators are of the same style and bear noticeably larger skirt lettering. They are aqua or light green and appear to be of Brookfield origin, circa 1900-1910.

Pettingell-Andrews Company

This organization commenced operation in Boston during 1888. Originally known as F.E. Pettingell & Company, their name changed to Pettingell Andrews & Company in 1889. Until the company became part of General Electric in 1927, Pettingell Andrews was a prominent electrical goods supplier.

Insulators were produced for Pettingell Andrews by an unknown glassworks, circa 1890-1900. All are CD 134 and are identical to Pennycuick insulators of the same design and threading detail. Most are aqua, bluish or lighter green and are distinctively lettered around the skirt. The majority of these rare insulators have been located in the vicinity of Boston.


Possibly of Boston area origin are a few CD 134 insulators lettered C.E.L.Co. on the skirt. The majority of these insulators are very similar in design and threading when compared to Pennycuick-threaded insulators of the same style. At present the origin of these is unknown. However, it seems likely that they, like Pettingell Andrews Co. insulators, were manufactured by James Pennycuick's August 11, 1885 patent process due to their characteristic fine, sharp pinhole threading. Most of these insulators have been located in numerous aqua shades. Unusual examples are in blue glass and vivid green. All are uncommon and have been located in different parts of the U.S.

Supplementing C.E.L.Co. specimens with Pennycuick threads are a very few that appear to have been made circa 1890-1900 in Brookfield molds. Most of these are aqua and are scarcer than their Pennycuick-appearing counterparts.

The initials on C.E.L.Co. insulators remain unattributed. It is quite possible the lettering represents Cambridge Electric Light Company. This firm was an electrical equipment supplier that operated between 1887 and 1892. Perhaps they had specially identified insulators made for them, as did Pettingell-Andrews about that time, and ordered them from the same glass company.

An interesting feature noticeable on all Pennycuick-threaded C.E.L.Co. insulators is the evidence of some previous lettering seen about where the initial C. appears. This "ghosting" is rather obvious and it is not known what the original letters were.


Unattributed at present are numerous CD 166 insulators simply lettered E.L.Co. on the skirt. All are of aqua glass and appear to have been well made, probably some time between 1890 and 1910.

A substantial number of these insulators were used on electric distribution lines in a New England city. Their initials do not represent those of the electric utility in that community.

There is some speculation that the E.L.Co. lettering stands for the Edwin Lewis Company. They were a prominent electrical supply distributor that was in business around 1900 in Boston.

C.S. Knowles "Boston" Insulators

The C.S. Knowles Company was a very well known supplier of electrical construction material during the early 1900's. Their offices were listed at 7 Arch Street, Boston and 120 Broadway, New York City. Factory listings were in Elmer and Trenton, New Jersey and Somerville, Massachusetts.

Knowles insulators are known in many designs that were commonplace during the turn-of-the-century. Of particular interest are two styles with BOSTON lettering, CD 282 and CD 292.5. These are also embossed 51/2" and 6", respectively. The significance of the "Boston" wording is not known. Although Knowles did not manufacture insulators, it is suspected that Brookfield and the Novelty Glass Company supplied them.

Boston's Specialty Insulators

CD 140

The first underground trolley system in the United States was placed into service around the year 1895. This historic railway ran below downtown Boston streets for a considerable distance. Originally, a portion of this run was uncovered and open to the streets above. A few decades later, the rail system was completely enclosed so that all track and the remaining stations extended through a continuous tunnel.

The direct current that powered this pioneer system was distributed through very heavy copper cables. Due to their excessive weight, these conductors were supported on large, oversized square wooden crossarms that protruded from the subway's walls at close intervals. Most insulators employed were CD 140 units, mounted on their large pins. An example of this can be seen in the display.

The Oakman Manufacturing Company (South Boston, MA) was commissioned to manufacture a great many insulators for this project. Brookfield also supplied some CD 140 insulators for this installation. The Brookfield units represent a small portion of the "Jumbo" insulators employed. These are unmarked and, although few, they have been located in an impressive assortment of color. These insulators range from light to dark olive green; from ice blue to rich turquoise; plus the most elusive ones in clear, purple and olive amber. All non-aqua unmarked CD 140 Jumbos are rare and highly desired by collectors. No CD 269 Jumbos or Brookfield CD 140's with JUMBO embossing are known to have been used along this railway.

Station remodeling and power distribution upgrades occurred through the years, resulting in the elimination of most CD 140 insulators from the Boston subway system. Virtually all insulators of this style in collectors' hands today were once used somewhere along that railway. Although the cables and insulators are long gone, a few of the original crossarms, outfitted with their pins, remain and can still be seen today in a couple of the older downtown stations.

CD 266

These units were known as the "Boston Cable" and "No. 5 Cable" in early insulator catalogs (notably Brookfield). These rare insulators are aqua, are prominently embossed No. 5 CABLE on the skirt, and have oversized pinholes like the CD 140 and CD 269 "Jumbo" insulators.

The CD 266 was produced around the turn of the century, intended for carrying heavy cables. The reason why the CD 266 style was nicknamed the "Boston Cable" is unclear. No significant quantity of them has been located anywhere, even in Boston.

CD 267.5

Nicknamed the "straight-sides," this unusual design was produced by the New England Glass Manufacturing Company exclusively for use on an eight-mile section of elevated transit line in Boston. Constructed during 1900 and dismantled during 1987-1988, this railway's trolley cars received direct current from heavy cables that were looped, without using tie wires, on bulky crossarms beneath the track's center catwalk. Spaced about twelve feet apart, the insulators were mounted on short stubby pins placed into their crossarms, as can be seen in the display. On some of the surviving specimens you can actually see individual crossarm wood grains around the insulators' base rims. On others, distinct cable strand rubs are clearly evident in the saddle groove. Frequent track vibration, along with the expansion and contraction of the cables, produced these distinctive characteristics. Some insulators broke or cracked due to this harsh environment.

In addition to the CD 267.5, many CD 267 insulators were installed along this railway. These were N.E.G.M.Co. and Brookfield-origin No. 4 Cable and unembossed specimens. The majority of CD 267 and all CD 267.5 insulators known today were used on this elevated railway line. Prior to its dismantling, many scattered groups of this line's insulators had been replaced through the years by more rugged units, mostly heavy white porcelain cleats.

The material included above was written and researched by Joe Maurath, Jr. of Abington, MA. Permission for the reprinting of this information is granted. References should give credit to the author.

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Written Wednesday, January 5, 2000; Last updated Wednesday, January 3, 2007