FieldSport&reg; 1/2x28 Thread Crush Washer Replacement Jam Nut Muzzle Brake Locking and Position Adjustement, All Steel, Black Steel, 5PC Pack Replace Crush washer for accurate and fine Alignment of MB Fully Re-useable not like crush washer 3/4 wrench opening 3/4 wrench opening Magnesium Phosphate Coating