The upset bolt is a typical fastener for the spool insulator, also called upset spool bolt or bolt upset.
There are two types of upset bolts namely single upset bolts and double upset bolts. The difference between them is the number of the forged plates at the insulator end. The insulator pin goes across one end of the thread. The forged plate will stop the insulator pin from moving down. In this way, the insulator pin is fixed on the end of the upset bolt to insulate the conductor and secondary service wires. There is a hole at end of the upset bolt with a steel pin to help stop the insulator pin from coming out. The finished is hot-dip galvanized per ASTM A-153 or equivalent. The main function of the spool bolt is to support the insulator pin for conductors and power wires going through. The upset bolt usually comes with a screw head type bolt with 2 regular square nuts, 1 lock nut, and 1 round washer.
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