The Viper Barrel Vise is constructed of 6061 aluminum. The bottom half is 1" thick, for added strength, when mounting to your work bench. All four hardened, threaded bolts have a support spring. These springs keep the top half from moving around during barrel insertion and removal. Each spring is fully captured on each end for stability. SPECS: Base is 7" x 3" with 5 3/4" c-t-c hole spacing for mounting; top plate is 3" square; four 1/2" bolts for clamping; and will accommodate 0.77" to 1.3" OD barrels. Mfg: Viper Bench Rest