1977 >> June >> Explanation of C.D. Consolidated Design Numbers  

Explanation of C.D. (Consolidated Design) Numbers
by N. R. Woodward

Reprinted from "INSULATORS - Crown Jewels of the Wire", June 1977, page 4


Due to increasing volumes of mail received by Crown Jewels from beginning collectors wanting to know what C.D. #'s are, I asked Mr. Woodward to write the following article. 

We all owe our sincere THANKS to Mr. Woodward for creating the C.D. #'s that we use so freely. Crown Jewels would like to suggest that if you don't have a copy of Mr. Woodward's "Glass Insulator In America Report", that you buy one as soon as possible, so you can fully understand what you are collecting. The "Report" contains more history on the glass insulator companies than any other book published to date. It also contains a cross reference number list and scale drawings, with C.D. numbers printed on the drawings. 

Mr. Woodward's "Glass Insulator In America Report" may be ordered from Frank Peters-Books, 495 Carr Ave., Aromas, CA 95004 (See ad page 42 this issue.).


The CD numbers were first used in cataloguing insulators in the early 1950's. Since various manufacturers used different numbers to identify the same style or design, the Consolidated Design Number system provided a single series of numbers that could be used to identify the approximate size and shape of any threaded pin type glass insulator. In practice, such a system was needed not only because of the various manufacturers numbers mentioned, but because in some cases the same manufacturer used the same number to indicate, at different times, two or more distinct styles. Also, the same style was sometimes given different numbers by the same manufacturer during different periods. Added to this is the fact that many insulators never had a style number that we know of; and the function of the CD numbers becomes clear. 

These numbers were developed as a private cataloguing aid and were so used for over ten years. In 1966, when insulator collecting was beginning to catch on, two pioneer Missouri collectors learned of the CD number system and asked permission to use it. In subsequent years, at least two other numbering systems were published and were used to some extent for glass insulators; but in the final analysis it has been the CD numbers that have become generally relied upon by collectors and have also been used to a limited degree in commercial identification. 

Many persons misunderstand the purpose of the CD numbers in that they expect them to describe the insulators exactly. This is not the case. Rather, the classification is approximate only; and in the case of such as CD #102 and #145, for example, made by a number of manufacturers over a period of many years, there is considerable variation. An attempt was made to include a typical or average drawing of each number in the 'Report"; but individual insulators that vary must generally be considered as being the CD number which is closest. True, there are without doubt more insulators that will need a new CD number. But after more than ten years of vigorous collector activity, these will be very obscure and rare items. 

In assigning the CD numbers, only the size, exterior contour and number of petticoats are taken into account. De- tails such as variation in pin hole diameter, number of threads per inch, drip points, interior or exterior ridges, metal caps or pin hole inserts, are not taken into account. 

The basic CD numbering system covers threaded pin-type glass insulators, those that are intended to be screwed onto a supporting pin. These are standard throughout North America and much of South America, as well as being used to a limited degree in other parts of the world. The numbers covering these are 100 to 375. Later additions were made by adding a decimal point and another digit, as, for example, 128.4, which is somewhat similar to 128. 

More recently, CD numbers have been published which cover the European and other pin-type glass which is intended to be cemented to a metal pin; and still later, other glass insulators which are not pin-types have been added. These numbering groups range from 700 upward. They were developed primarily as an aid to the Milholland publications, and, unfortunately, they are not as well organized as are the basic ones, due to our very incomplete knowledge of some of the fields covered. However, these too have served their purpose as a tool of identification and are the best we have in these areas.

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