5/8" Crush Washer
This is a 5/8" crush washer used for mounting some types of muzzle brakes and fits barrels with 5/8x24 threads which are standard for .308 cal/7.62mm barrels, .300 BLK barrels and some 6.8 SPC barrels. Many new muzzle devices come with the necessary washers, shims or nuts to mount them with. But some models don't and sometimes replacement washers are needed if installing a muzzle brake on a different gun.
Crush washers are used to allow the shooter to tighten the muzzle device on the barrel while giving it precise alignment if needed. Crush washers crush down while tightened up to a full turn. They are designed for the narrow side to be against the barrel shoulder and the wide side to be against the muzzle device. Has a black oxide finish.