The newly updated LM4 bolt catch is made of hardened metal and accepts a bolt catch spring, part 42, which is sold separately. The bolt catch fits all LM4 variants, including the LM4C and LM4 RIS, as well as the standard LM4 RIS.
This part also appears as part 16 on the PTS MKM AR-15 and PTS MML Maten diagrams. Most internals for the PTS MKM AR-15s are compatible with LM4 parts.