Howdy, folks. Time to tax your brains and research capabilities. I have two questions concerning this part. 1. On which part of the US Rifle, Cal. .30 M1 does this marking appear. 2. What manufacturer and era is this part from? The winner becomes the "king of the hill" and is responsible for posting the next quiz. Those more experienced collectors among you I ask to email me your answer at email@example.com to allow the newer collectors to learn and play.