These back plates are manufactured thicker for use with adjustable chucks. This extra thickness allows a large step to be machined on the front of the plate for use by the adjusting screws on the chuck. The remaining material safely supports and secures the chuck. Both plates are supplied with a bore of 1.968”. All South Bend back plates are made of fine-grain cast iron. Whether you need a blank or semi-finished back plate, you can depend on the quality and precision you’ve come to expect from South Bend.