Pony insulator, 1933
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Alexander Graham Bell invented twisted-pair telephone wiring in 1881 by to stop interference of electrical and telephone lines on the same utility poles.
The Hemingray No. 10 "pony" insulator was developed to accommodate this new wiring system, with square grooves set close together and a thicker, sturdier construction than earlier communication insulators. The No. 10 soon became the standard communications insulator.