The aac blackout flash hider for 51t mounts is an extremely efficient design that effectively eliminates muzzle flash, even on short barrels.The open-end, 3-prong design of the blackout is inherently stronger than 4-prong units and is not subject to the wear and erosion commonly encountered with closed-end designs.All of aac's blackout flash hiders are machined from high strength aerospace steel alloy and coated in a hard, durable, corrosion resistant scarmor finish.Rocksett includedModel: Blackout Flash HiderMaterial: SteelThread Pattern: 5/8"-24 tpi