Pintype electric insulator, ca. 1916
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The "pintype" insulator, with a socket in the base that screws on to a threaded wooden or metal "pin" mounted on the utility pole, was patented in 1865.
Earlier insulators were secured to the pins by various means (padding with burlap, or perhaps sticking down with tar).
Insulators keep the current in the grid and prevent it from "leaking" where it would be wasted or creating a hazard.