Parkerized aluminum thread protector designed for the Yankee Hill Machine quick-detach sound suppressor mounts. Protects large ACME threads from damage and dirt when the suppressor is removed. Works with all YHM quick detach flash suppressors and muzzle brakes. Please note this will not fit standard 1/2"-28 AR-15 barrel threads. It is only for the coarse threads found on Yankee Hill quick-detach flash hiders and suppressor mounts.