This is mil-spec steel coiled roll pin for the Mk11 Mod 0, the M110, and M110 Model K, and most gas blocks that take a free floating RAS or URX, URX-II, URX-3 and URX 3.1.
Note: Mk11, M110 and some other SR-25 gas block also two taper pins, here.
part number: KM-21073
