Just recently I found a split bridle ring lag insulator embossed Patent Applied For. Any time I find something like this I figure there has to be a patent somewhere. Alas I couldn't find one for the porcelain split ring style, just for a metal ring style patent D31,861 Nov. 21,1899 (neat that it was issued a day before my birthday 11/22/1972 only in 1899 HaHa). The porcelain split ring styles started making an appearane during the mid 1930's. Many companies produced them but it's hard to find ones that are marked. Here is a picture of marked split ringed pieces I have. The top one is a metal enamed coated piece to insulate it. Below that L-R Large Knox, next is an unmarked Knox loop style, next T(thomas) 2, between that small star (StarPorcelain Co.),T large size, next U.S.A. (made by Porcelain Products Inc.), last P (Porcelain Products Inc.) In the adjoining picture Patent Applied For, below that HP (Hamilton Porcelain Co. Canada Ltd.), Next Diamond shape (Diamond Expansion Bolt Co.), Small embossed Diamond Exp. Bolt Co. NY., Between that N. Slater Canada with EP lightning bolt in a circle design, next Diamond Exp. Bolt Co. NY. re-embossed, Last N. Slater Canada H.P.B.