Shars 8 4 Jaw Self Centering Lathe Chucks with 2 Sets of Jaws +. 0039 TIR Certificate New. Each high quality chuck comes with a certification that documents TIR. Center hole: 2.56. Bolt Circle Diameter: 7.087. Input Torque: 250 Nm. Semi-steel chuck body made from high quality cast iron. Each pinion is ground and hardened to HRC 43. Both sides of the jaw teeth and guides are ground and hardened to HRC 58-62. Each set of jaws are serialized in their own set. A serialized set of jaws are then finished, ground, and lapped on their designated chuck body which will be the same chuck body on the final assembly to achieve a greater accuracy. Before assembling the jaws to its designated chuck body, the jaws finish machining is performed on a close tolerance state of the art CNC machine from Japan. The scroll plate’s thread flank are ground on both sides to achieve tighter contact with the master jaw. Each chuck has gone through rigorous accuracy and repeatability inspection by clamping and jamming multiple random testing rods or rings. Accuracy is maintained for the entire clamping range Clamping Range. Internal Jaws: Clamping Range: A-A1 0.157-3.346″ Jamming Range: B-B1 2.559-7.874″ External Jaws: Clamping Range: C-C1 2.559-7.874. D2 Mounting Hole Bolt Circle Dia (inch). 2 set of jaws: inside jaw set and outside jaw set. 3 piece of mounting screws for the lathe chuck back plate. If you need to speak to a sales person feel free to call. We are open Monday through friday 8:30 to 5:00 est.