8" - 4 jaw self-centering lathe chuck with D1-4 back mounting adapter plate. with 2pcs top & bottom tongue groove reversible jaws. jaws ground and hardened. PRECISION SEMI-STEEL BODIES. TOP QUALITY. STRAIGHT RECESS OR PLAIN BACK SPINDLE MOUNTING. 2-5/8" THRU HOLE DIAMETER Back mounting recess dia. 165mm Back mounting bolts circle dia. 180mm D1-4 camlock pins and screws are included. On Jul-26-11 at 15:09:20 PDT, seller added the following information: