This lead thimble is used to allow an insulator with a 1 3/8" diameter pin hole to be reduced to a standard 1" diameter pin hole. Thimbles were also made of iron and were threaded with machine threads for installation on machine threaded bolts and rods. Note that this thimble also has a cork cushion at the top of the pin hole. Another way to look at this is that the thimble was used to enlarge the thread area of a standard threaded pin to allow the installation of an insulator with the larger 1 3/8" pin hole. Also note that the thimble is constructed of a galvanized metal inner thread core with the lead cast in a mold around the core to create the larger diameter threading.