On October 14, 1851, John Yandell was issued a patent for a telegraph insulator. This insulator was similar to the types of glass blocks outlined previously, but differed in that it was made in a cylindrical shape. It also could be placed into a pole or bracket with an appropriate opening for the insulator to be inserted. The CD 1012 has a slot at center for holding the wire and is similar in shape to the original Yandell patent drawing. It would fit snugly into the opening made for it in the pole, crossarm, or bracket. A small indention or notch is also molded into the flanged end so as to receive a nail, driven through the wooden structure to help in preventing the insulator from accidentally slipping out.
CD 1012 known as the Yandell patent insulator.
A modified variety of the Yandell design has a diameter which is larger at one end with a tapered channel through the body of the insulator. This is the CD 1014 style.
CD 1014 with wooden augured bracket. (Smithsonian Institution)
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Unless otherwise noted, photos by Larry Novak or Bob Berry
This is the CD 1010, and is similar in design to the CD 1014 but differs slightly.
Rather than having one end that flares out form the main body of the insulator, this one has a more uniform taper from one end to the other. These cylindrically-shaped blocks have been located in California and most likely date from the 1850's.
CD 1015 is a uniformly cylindrical block.
These blocks dramatically taper from each end to a narrow opening in the middle of the body's length. This design provided a very short point of contact for the wire to touch the glass. This cylinderical block has no notch for attachment as the CD 1016 does. It, too, dates from the early 1850's.
CD 1016 is a uniformly cylindrical block with a perpendicular round notch on the outside wall of the insulator.
The glass cylindrical CD 1016 insulator would be installed into a hole drilled through a crossarm. The exterior notch would receive a rounded wooden peg which would help to secure the insulator in position in a crossarm. This insulator is one of two known to the hobby. I believe both examples came from western Pennsylvania where they were used in the construction of an early telegraph line in the area..