The metal LM4 hop up cylinder acts as the primary housing for the LM4 hop up system. It appears as part 4 on any LM4 diagram, but is also part 4 on the PTS MKM AR-15 and PTS MML MATEN. Most internals for the PTS MKM AR-15s are compatible with the LM4 PTR Series.

Weight .1 lbs
Dimensions 1 × .5 × .5 in