The Starrett KA19 Hole Enlargement Arbor allows diameters to be enlarged by attaching a saw of the same size to that of the existing hole. This saw then acts as the pilot for the larger diameter saw attached to the arbor.

Specifications:

Compatible Holesaws: FCH, DCH, TCT Multi Purpose, CT & Diamond.
Compatible Threads: 1/2in x 20 & 5/8in x 18.
Min. Hole Enlargement: 4.7mm (3/16in).