There is a series of company names that made this style of grip adapter, not necessarily in order. Mershon, Fray Mershon and Pachmayr. The S&W branded ones were made for sure by Mershon and Pachmayr, but possibly by all three. These were not different companies but successor names for what was a continuous enterprise. The hole for access to the strain screw was drilled after-market by a previous owner. Except for the hole and S&W trade mark just what is it you thought was strange?


Here is a thread with more: Puzzle -grip adapters - Mershon, S&W, Pach