17-4 PH Atlas and Atlas XL compatible Plan B compatible Black Nitride finish (67 HRC Surface hardness) Shims not included, if you would like to specifically time this, shims will be required. Note: your barrel may require a shim if the manufacturer did not put a thread relief on it. Weight: 2.05oz Length: 1.74" Length Added: 1.115" These fit Plan B type mounts. Always use an alignment rod to ensure that the entire system is set up correctly. Make sure all surfaces are cleaned and the muzzle device has been torqued and Rockset to the barrel. Use on a Q can voids your warranty, be warned. Torque the muzzle device to approximately 30 ft lbs. Make sure the muzzle device is square against the shoulder. When setting the silencer on the muzzle device, ensure that the threads and tapers are clean. Torque the suppressor to 10 ft lbs. Ensure alignment. Enjoy. The nitride finish does lead to a tighter seal, with that said, it is extremely important to torque and rockset your muzzle device to the barrel properly.