Watchtower Firearms Compensator Muzzle Brake 5.56 Flat Black. Manufactured from 4140 low-alloy steel and is available in all F-1 Coatings PVD finishes. Specifications for Watchtower Firearms Compensator Muzzle Brake: Manufacturer: Watchtower Firearms Caliber: 5.56x45mm NATO Finish: PVD Coated Fabric/Material: 4140 Steel Threads per Inch: 1/2x28 Length: 2.25 in Weight: 2.55 oz Fit: Flat Features of Watchtower Firearms Compensator Muzzle Brake Stainless in 316SS all others in AISI/SAE 4140 low-alloy steel; Package Contents: Watchtower Firearms Compensator Muzzle Brake Watchtower Firearms CMB-556-FB: Compensator Muzzle Brake 5.56 Flat Black