HSS bi-metal hole saw, Ø 21mm. Bi-metal hole saws feature hardened teeth made of high-alloy high-speed steel with 8% cobalt content, significantly increasing tool life. They provide faster and smoother cutting due to a new type of teeth with an irregular shape and pitch, resulting in less vibration. Optimized for use in cast steel and gray cast iron, stainless steel, structural steel, aluminum, bronze, copper, PVC, acrylic glass, and wood. Maximum cutting depth is approximately 35 mm. Thread for hole saw Ø 14-30 mm: 1/2"-20 UNF. Thread for hole saw Ø 32-152 mm: 5/8"-18 UNF. Use hole saws only with the appropriate arbor and center drill.