RCM HK Style 21 Trunnion. As with all RCM products there are no finer US made trunnions available. The factory Trunnion was put through destructive metal testing to determine proper material and heat treat. No corners cut in making these. Matches up perfectly with our 21 Barrel. Some of the kits that are coming in have worn out galled up Trunnions that should be replaced. Don’t hesitate on installing a new one.