CD Numbers Explained

This section covers the following:

What is a CD number?

Consolidated Design (CD) numbers are assigned to specific shapes of pintype glass insulators, regardless of the manufacturer, embossing or style number. Minor variations in size or detail do not affect the CD number assigned to an insulator. The CD numbering system is designed to provide a concise way for collectors to refer to these shapes. This system is universally adopted by all collectors, and is used extensively in all aspects of the hobby.

CD numbers start at 100 [1], and may be followed with a decimal point and a single digit. CD 154 and CD 128.4 are examples. CD numbers are grouped into ranges of numbers, or CD styles, that represent insulators with similar characteristics. Generally within a CD style, a smaller CD number represents a smaller insulator. A more detailed breakdown of these CD styles can be found in this section. Note that lightning rod and radio strain insulators are not included in this CD numbering system.

[1] With the recent addition of battery rests to the CD numbering system in 2003, CD numbers start at 10, with the range 10-99 reserved for battery rest insulators.

How to identify the CD number of an insulator

Associating a CD number with an insulator often requires the use of reference material. Identification of a CD number is generally done by determining its CD style, and then comparing it with photographs or drawings until a match is found.

Tip: The Manufacturer and Style number to CD Chart can be used when the insulator has a style number, to determine one or more possible CD numbers. The price guides available today have these charts. Some more common CD shapes with photographs, history, and usage can be found under the Insulator Profiles section.

Price Guides with manufacturer style number charts are:

A number of threaded insulators and most threadless insulators are not embossed with a style number. These will require identification with photographs or drawings. Even when identification can be made by a chart, it is still useful for the beginner to be able to confirm their initial assignment by looking at a photograph or drawing.

Reference books with photographs and/or drawings:

How are CD numbers assigned?

A separate article CD Assignment Guidelines provides details on this.

A history of the CD numbering system

[This section is under development]

General breakdown of CD numbers

The information from this section was compiled from The Glass Insulator in America, 1988 Report, Glass Insulators from Outside North America, and the 2003 Price Guide for Insulators: A History and Guide to North American Pintype Insulators.

CD numbers are broken down into a number of major groups:

Battery rest insulators:

Pintype insulators:

Miscellaneous non-pintype styles:

Specific breakdown of CD numbers

CD 10 to 99 Battery rest insulators:

CD 100 to 375 - North American threaded pintype insulators

These CD styles are generally grouped by the number of petticoats the insulator has (single, double, triple), and the type of wire groove and placement (side wire groove, saddle groove, cable top).

CD 376 to 699 - Foreign threaded pintype insulators

There are a number of foreign CD styles that are the same as the North American styles. In these cases, the CD assigned for the North American insulator is used.

CD 700 to 799 - North American threadless pintype insulators

CD 800 to 999 - Obsolete Foreign pintype insulators

CD 1000 to 1199 - Glass blocks, spools, dead end insulators and miscellaneous styles

This section includes both North American and Foreign styles

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Last updated Thursday, December 14, 2004