This is the perfect addition for a Mk12 sniper rifle clone build, together with the #22 TRR, this is the top of the forward scope ring for the mounting of a PEQ, laser range finder or RMR sight. The Mk12 Mod 0 was famous for this ring cap with the TRR, as were certain Navy RECCE builds. This is a hard to find item, ideal for Mk12 collectors and clone builders. Finding quality clone parts is not easy.
from ARMS:
For use on all A.R.M.S.® #21™, #22™, and #35™ Ring saddles.
This unique ring cap was designed to expand the standard use of a cap normally only holding a scope in position, to that of allowing modular enhancements on various conventional optics by simply removing the standard cap and installing the tactical cap using the same socket head screws.