17-4 PH H900 Atlas and Atlas XL Compatible Plan B Compatible Atlas Adapter Overrun Approximately 1.050a ^2 Atlas XL Adapter No Overrun H900 Wheat Finish (Variations Exist) 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. These fit the plan B type mounts. This is an updated version that has larger wrench flats on the rear. 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 15-25 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.