Blackout Defense 1/2-28 Keymo FG42 Brake Black. The KeyMo FG42 is compatible with Dead Airs KeyMo-equipped silencers. Specifications for Blackout Defense Keymo FG42 Brake: Manufacturer: Blackout Defense Finish: Nitride Fabric/Material: 17-4 Stainless Steel Features of Blackout Defense Keymo FG42 Brake In-house heat treated to condition H900 for a through-hardness of 45-47 HRC 17-4 stainless steel that is heat treated to condition H900 exhibits 14percent higher ultimate tensile strength over hardened 4140 steel Package Contents: Blackout Defense Keymo FG42 Brake Shim kit Blackout Defense MUZZLE-1/2-KEYMO-FG42-BLK: 1/2-28 Keymo FG42 Brake Black