Here is a comparison of a railway dead end spool spool (clamp band ) on the left and a standard primary dead end spool on the right . The unit on the right is marked Victor and has a glaze welded top skirt ... all of these large spools are scarce to very rare but I think the railway ones are the most unusual as the majority of AC railway cantanary construction in America began in the suspension insulator era after these spools fell out of favour . these large spools were mostly gone by the 1910-1912 era .