Fred Locke liked to mix and match different molded clay parts of various uniparts glazewelds and multiparts to come up with various combinations of insulators. Because of his early use of applied crowns and glazeweld sections quite a wide variety of different insulators were made using the same basic parts . The Victor factory soon discovered the the amount of extra work that went into assembling an insulator like the U-939 from three septate parts could be eliminated by making the same basic design in one part and green trimming the tie wire groove like the U-441/ 447 etc.
These all share the same applied crown. U-675a (missing it's top platter) U-669, U-675 and U-939 all share the exact same applied crown . All of these were late 1900-1901 production