An insulator pin is used to hold the insulator that is mounted on top of it in a vertical position. The use of steel is required wherever the pins must be extra long and sturdy due to high voltage and when the conductor is under severe tension.
Insulator pins are bolted onto a crossarm and the insulator is then screwed onto the top of the pin. The wire is then typically attached to the insulator by being wrapped around it. This isolates the wire from it's physical support and as the insulator is made out of a non-conductive material, prevents any significant damage in the event of an electrical failure.