Bone Black Hammer Brass Knuckle. The structural design of this belt buckle knuckle has been designed to maximize durability and minimize the overall weight on your belt. The brass belt hole pin fits snugly on a belt and intimidates a target in seconds. The Bone Black Hammer Brass Knuckle is electroplated black, so it is resistant to chipping and scratching. Total length is 4.25 inches, with four finger holes, steel construction, and includes a belt hole pin. Overall Length: 4.25 Inches. Construction: Steel, Four Hole. Finish: Electroplated, Black. Includes: Brass Belt Pin.