Colonel Mustard jam nuts / lock nut. Use as an alternative to a crush washer to lock your muzzle brake or flash hider in place. Screws onto standard AR-15/M4/M16 ½" x 28 threaded barrels. This thread is also commonly used on .22 LR, .22 Mag and .17 HMR rifles. CMMB75-1/2x28JN.
Part Number: CMMB75-1/2x28JN