John S.Lapp patented a unique dead insulator design in 1905 that was manufactured by Locke and later others useing patent # 795,521. this was an improvement on Fred Locke's dead end spool design that used two shells cemented with Sulfur cement .[id=429409535] The inner shell is taperd to a narrow area at the point where the line conductor weraps around the insulator . It also has a petticoat on the inside of the top hole to increace leakage distance . several difrent sizes were made useing this patent the largest being the # 606 with 10" wide skirts . Pictured here is the smaller #603 spool ( 8"x 8 1/2 " ) for use up to 23kV Both the larger and smaller spools are very rare in collecor hands with only a few known to exist . These large spools fell out of favor once reliable dead end suspension bells became available after 1910 http://reference.insulators.info/patents/detail/?patent=U795521 this spool was bought on eBay and was unfortunately damaged in transit .