8" - 4 jaw self-centering lathe chuck W. 2-1/4"-8 adaptor back mounting plate with 2pcs top & bottom tongue groove reversible jaws. jaws ground and hardened. PRECISION SEMI-STEEL BODIES. TOP QUALITY. 2-5/8" THRU HOLE DIAMETER Back mounting recess dia. 165mm Back mounting bolts circle dia. 180mm 0.003" TIR