U-710. There are three different incuse stamps. One has the Imperial crown logo, one is a date stamp, the third indicates that the insulator was manufactured by Imperial Porcelain Works in Trenton, New Jersey. white porcelain, 3 skirt, recently recovered from a suburban Chicago power house, mint condition. $75+postage.
U-710 Imperial Porcelain Works, 3 incuse marks, sulfur-cemented metal cap, $75+postage