The ProMag Armorer's block locks into the lower receiver of an AR-10 style rifle and can be clamped into a vise for gunsmithing. The block is black and constructed from injection molded polymer. Double sided design fits ArmaLite, DPMS, Remington, SR-25, and many other variants.FeaturesHeavy duty block clamps into the magazine well of the lower receiverHelps to prevent damage or movement during repair, assembly and cleaningDouble sided design fits Armalite, DPMS, Remington, SR-25, and many other AR type riflesMade of injection molded black polymer