Center Hole Diameter: 2.95. For use gripping odd shaped work. Chuck includes one set of reversible jaws. Four jaws allow a square component to be perfectly centered to the chuck while achieving maximum gripping force.
Jaws are made of high quality carbon steel, and hardened. Thrust bearings and operating screws are made of case hardened steel. Included 1 set of reversible solid hard jaws.When you pick fully machined back, please follow the following instruction. How to process back plate to guarantee Chuck's T. All back plates have 0.04 allowance, please measure the size of Chuck's D1 before process your back plates. The size of back plates's D1 should be a little bit smaller than the size of Chuck's D1. Because the gap between back plate and chuck is smaller, chuck's TIR is better.
No gap is the best. You would not need to drill any mounting holes but you will need to turn the shoulder down. 040 to match the back of the lathe chuck to make the chuck & back plate more concentric with the lathe spindle.
When turning the shoulder of the backing plate, ONLY TURN THE SHOULDER OF THE BACKING PLATE WHEN ATTACHED TO THE LATHE SPINDLE. If you use a chuck to clamp the backing plate and then turn it, the backing plate will not be true to the lathe spindle and will have more runout than specified when the chuck and back plate are put together. Why 12" back plate size is smaller than 12" chuck? Bolt Circle Diameter is 6.496 , then the back plate will match to the chuck. Bolt Circle Diameter is only 6.496", there is no need the back plate has to be 12" any more.The item "12 4 Jaw Independent Lathe Chuck Plain Back TIR Certificate 2 Set Jaw" is in sale since Friday, August 23, 2019. This item is in the category "Business & Industrial\CNC, Metalworking & Manufacturing\Workholding & Toolholding\Workholding\Other Workholding". The seller is "discount_machine" and is located in Saint Charles, Illinois. This item can be shipped to United States.