Here is some more Duplex Streetlight insulators in my collection. The top picture is of two Hubbard and one Pierce split knob style made by Hubbard & Company. The Peirce one is also marked PAT APPLIED FOR on the metal front. They had a patent US 1,788,245 1/6/1931 for these. The bottom picture is of two different pieces made by Seyler Mfg. and Construction Co. They both have an embossed S on the metal shank of the insulator. Seyler was a distributer for Locke Insulator Co. and their own brand. Locke probably made the porcelain parts for Seyler. I have many Seyler, Locke and General Electric wire holders and spools that share the same shapes and catalog numbers.