This mine insulator utilizes another type of attachment. A cast collar to fit the lugs on the spindle or shaft portion of the pin. After the insulator is slid onto the spindle the collar is also placed on the spindle and rotated 90 degrees so the lugs will seat into the grooves cast into the collar. This method of attachment is one of three that I know of. The other of this type uses a compression spring at the back of the insulator with lug locking grooves formed in the insulator. The third is the standard thread split pin with the hollow center.