Century  5866 Shark Tooth Arbor Attached Bi-Metal Hole Saws, 4-1/8-Inch Suggested speed RPMs are for cutting mild steel; decrease RPMs by 30 percent for cast iron; increase RPMs by 30 percent for bass and aluminum Can be used in portable electric drill machines lathes and milling machines Extra deep 1-7/8-Inch cutting depth on the arbor attached shark tooth hole saws 3/8-Inch attached arbor Made in the USA