Luth-AR 308 Crush Washer 5/8-24

A crush washer is what times a muzzle device. You thread the brake or flash hider on, snug it against the washer, and keep turning until the device sits where you want it while the washer collapses to take up the gap. This one is cut for 5/8-24 threads, the standard pattern on 308 barrels.

Crush washers are a consumable. Once one has been compressed it has given up most of its travel, so plan on a fresh washer any time the muzzle device comes off and goes back on. They cost almost nothing and they are the difference between a brake that sits level and one that does not.