This muzzle brake is designed to fit with any 7.62mm or smaller caliber rifle with a muzzle thread of 5/8-24. It is made of stainless steel and black nitride treated for long life. It is also supplied with a lock nut to facilitate timing without the need of a gunsmith. Just spin the lock nut on, all the way to the back of the thread, and then run the brake down against it. Back off the brake to the desired clock position and run the nut up to it, then back off the brake 1/8 turn more, run the nut up to it again and then tighten the brake against the nut with a wrench on the supplied wrench flats. Done. No muss, no fuss. Brake ships with lock nut in the package.