The Starrett A19 'Oops' Arbor can be used in conjunction with: A1, A2 or A10 type holesaw arbors. Replacing the pilot drill, it allows diameters to be enlarged by attaching a saw of the same size to that of the existing hole, this acts as a pilot for the larger diameter saw. Works with the following holesaw type: (SH) Constant Pitch HSS Bi-Metal, (DH) Dual Pitch HSS Bi-Metal, (MPH) TCT Multipurpose, (CT) Carbide Tipped and (D) Diamond Grit. Minimum hole enlargement is 4.7mm (3/16in) between the pilot saw diameter and the cutting saw diameter.