The AR-STONER LR-308 Lower Receiver Vise Block is made of Solvent resistant polymer construction for strength & durability. It allows for safe mounting and will help to prevent any type of distort or damage to the Lower receiver. Great to use when performing your regular maintenance, repairs or weapon assembly. Fits into the magazine housing from either the top or bottom, and the magazine catch will securely lock your receiver into place in the vise. Note: Fits .308 Mag Wells for most DPMS/AR-10 style rifles