Heavy-duty vise block takes all the clamping force, so your expensive lower receiver won't get scratched, distorted, or otherwise damaged. Insert block into the mag well, just like an ordinary magazine, then clamp the other end in your bench vise. The magazine catch locks to the block, safely and securely holding the rifle for assembly, disassembly, cleaning, or repair. Double-ended design fits ArmaLite AR-10, Bushmaster .308, DPMS Panther LR-308, and Remington R-25. Does not fit Rock River Arms lower receivers. Machined from rugged, durable, chemical-resistant Delrin polymer; will not mar or scratch weapon's finish. Mfg: Brownells SPECS: Machined Delrin, white. 5-1⁄8" (13cm) high, 3" (7.6cm) wide, 1" (2.5cm) thick. Fits most AR-Style .308 rifles except Rock River Arms.