Morse.
177368 MHS Advanced Hole Saw, 2-1/4 in dia, 1-15/16 in D Cutting, M42 HSS-Co 8 Cutting Edge, 5/8-18 Arbor Required. Morse Hole Saw, Advanced, Series: MHS, 2-1/4 in dia, 1-15/16 in Cutting Depth, 5/6 TPI, 5/8-18 Arbor, 1/4 in dia x 3-3/32 in L Drill, M42 HSS-Co 8 Cutting Edge, Bi-Metal Body, Toothed Cutting Edge, 75 to 230 RPM, 1/2 in Chuck, Hex Shank, 7/16 in Shank, Use Arbor: Ma45Ps, Red, Applicable Materials: Machinable Metal, Nail Embedded Wood, Plastic, Stainless Steel Alloy and WoodThe All New Advanced Bi-Metal Hole Saw by M.M.