This screw chuck has 3 different diameters of backing plate to give optimum support to a wide range of projects. The screw is designed to bite into the wood. To use the chuck, a 1/4" diameter hole is drilled 1" into the blank which is then screwed onto the chuck until it beds out against the backing plate. If the collar screws on the chuck hub are removed, the remaining backing area is 1-5/8" in diameter. This is the smallest size this chuck can be. The collar can be threaded onto the hub with choice of creating a 2-1/2" or 3-3/4" backing plate. The area of the turning that beds out against the chuck needs to be flat. This chuck is precision machined out of steel.
Each chuck is direct threaded for the size needed.