Great option since factory HK UMP stocks are hard to find and expensive. The HDPS HK USC/UMP Stock Block "C" Each unit comes with the new push pin design. This is the type For use with the ACE hinge part number FSM-TB (push button folding stock) and non folding push bottom (pignose), several other options are available as well. This is just the transition piece to add a variety of US stock options to your USC conversion. Each stock block is the latest US made HDPS production part available with the new scratch resistant coating & finish & latest generation upgrades.