Starrett KA19-N "Oops" Arbor, Hole Enlargement Arbor. Replaces the pilot drill in any Starrett A1, A2 or A10 type arbors. Replacing the pilot drill, the KA19 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 that is attached to the arbor in the normal way.