are you sure it didn't come out of your trigger guard? see the two roll pins that hold it on, they are about that size. could also be the rollpin that holds your gas tube to the gas block. its hard to say, i dont have an LMT anymore, and some brands of AR use pins to hold certain things while others use roll pins but based on the size compared to the coin id say trigger guard pins or gas tube pin, unless your extractor or ejector was held in by a rollpin
if i type rollpin one more time im going to need a drink lol