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https://centerfirereserve.com/product/rearden-fhd-nitride-flash-hider/

REARDEN FHD FLASH HIDER – NITRIDE

The Rearden FHD Flash Hider with a nitride finish is a 3-prong flash hider that also functions as a suppressor mount, specifically designed for the Rearden Atlas, Atlas XL, and Helios QD suppressor mounts. It utilizes the Atlas/Plan B mounting system, which combines a taper and external threads for secure suppressor attachment. This allows for a compact and efficient setup, enabling users to quickly attach and detach suppressors. 

• Atlas and Atlas XL Compatible
• Plan B Compatible
• Atlas XL Adapter No Overrun
• 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.

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 Rocksett 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. The nitride finish does lead to a tighter seal, with that said, it is extremely important to torque and Rocksett your muzzle device to the barrel properly.