Stromberg Carlson was a telecommunications equipment and electronics mfg. Co. established in Chicago in 1894. This U-47, wet process, porcelain insulator is [ r-e ] recess- embossed with their name and the mark HP I find no reference to the mark HP. Perhaps a manufacturers mark from a foreign Co. With only 3 reported in the "Value Guide" [seq No. 243] I think this is an under rated and novel insulator. At the recent YPCIC show in Enfield Ct, it drew much interest.