N. R. "Woody" Woodward is the author of THE GLASS INSULATOR IN AMERICA, 1988 Report and developed the Consolidated Design Numbers identification system for glass insulators. 

The first question was submitted by Ken House of Deltona, Florida.

QUESTION: I am sending a photo of an insulator that came out of a collection from North Carolina. It measures 2-1/4" high and slightly over 1-1/2" in diameter at the base. Would you help me identify this small insulator and its use?

The IN-56 insulator was made by Owens-Illinois for the military during World War II years. It is composed of the double groove glass insulator with a lag screw cemented into the pin cavity. It served to string telephone or low voltage electric wires on any wooden support, without regard to the particular style of line construction in the area. Thus it was suitable for speedy construction of temporary lines or for repair of existing lines which had been damaged. 

Nothing is known of the extent of its actual use. These insulators came to the attention of the public when numbers of them appeared on the military surplus market during the 1950s. They were used by farmers for electric fences or rural phone lines.

Although it has a threaded pinhole, the IN-56 is not properly a pin-type insulator since it was intended for use only with the lag screw cemented in place. Since a metallic cement with a low melting point was used, some of these have been removed from the lag screw and give the appearance of a small pin-type insulator. 

There is also a similar insulator made from brown glazed porcelain. These seem to be somewhat less common than the glass ones. Perhaps some of our porcelain people know who made those?

Ken House's IN-56 had the lag screw removed. Above is how the
 complete insulator was assembled for affixing to any wood surface.

The following questions are from Gary Short of Chapmansboro, TN.

QUESTION: I have a beehive style insulator which has large threads on the outside of the glass. It is marked "Patented Oct. 8, 1907". I am not familiar with its patent.

The insulator marked PATENTED OCT. 8 1907 is probably a common one, although we can't be certain until we know for sure which CD number it is. Other than CD 147, which is common, there are two differing styles which carry this patent date; and they are quite scarce and desirable as collectors' items.

That patent was issued to John C. Barclay, who was chief engineer at Western Union during those years. These insulators were designed for use with the heavy iron wire that was standard on telegraph lines prior to World War I. On those lines, the tie wire consisted of a single U-shaped loop which was twisted one and one-half turns around the line wire on either side of the insulator. 

As you will note, the external thread runs opposite to the internal one. The theory was that as a damaged insulator was removed from the pin for replacement, it could be simultaneously removed from the wire by a slight upward pull on the line while turning the insulator. The new insulator could be installed in the same manner, without the need to remove and replace the tie wire. Millions of these insulators were supplied Western Union by both Brookfield and Hemingray. If the lettering is exact as you have copied it, your specimen would be a Hemingray.

QUESTION: Also I have a rubber insulator embossed with Continental Rubber Works, Erie, PA. USA plus a patent number. Is it uncommon?

The rubber insulators, of which you have found an R-4, were designed by Western Union during the 1930s and were used extensively by them and by many of the railways. They were made of a special compound containing wax which, as the insulator was heated during warm weather, would gradually migrate to the surface to avoid drying and cracking of the rubber and maintaining a good insulating surface. These insulators did not have an unlimited life. If yours is quite old, the surface may be dry and checked, indicating the insulator had outlived its best years. Also, surprisingly, in some parts of the country squirrels found them appetizing; and in wooded areas one may find, rubber insulators partially eaten away. 

The rubber insulators were primarily intended for use in areas where vandalism was high and breakage of glass occurred on a regular basis. It was understood that they did not have the unlimited life span of a glass insulator.

QUESTION: The last insulator I have is one with a hole through it. It is 2-1/2 inches tall, 2-7/8" wide, the wire groove is 3/8" deep by 5/8" wide. The pinhole is threaded for a 1" pin.

The third insulator you described was made under the Robert G. Brown patent of November 23, 1886. There were two styles made, the Brown Pony (CD 187) and the Brown Deep Groove (CD 188). According to the measurements you gave, you have a specimen of the latter, the less common of the two. These were made for use with a special pin, the upper part of which was the same as a regular pin; but the lower part extended below the bottom of the crossarm and was also threaded. The Brown insulator was used thereon. When an arm was assembled with Brown pins, its capacity for wires was doubled.

The reason for the through pinhole is so that if water gets into the insulator it can drain through and not remain inside the threads. Should that happen, the insulator will crack if the temperature drops below freezing. The top of the insulator was rounded to shed water and was supposed to fit closely under the crossarm, But the open bottom was a double safeguard. 

Most of these are embossed PAT'D NOV. 23d 1886. Often they are difficult to read; but check your sample for this marking.

A page from Edwin C. Lewis Catalogue, c1908,
 showing Browns with an assembled Brown pin.