The Starrett Fast Cut Bi-Metal Hole Saws contain an extra cobalt HSS tooth material for enhanced heat and wear resistance, along with a new 5.5 TPI positive rake tooth design, to ensure a smoother and faster cut when compared against our previous Constant Pitch Hole Saw. Specifically designed to cut stainless steel, metals and mild steel sheet, Fast Cut Saws will also cut through wood, plastic, plaster and other materials. Extra Cobalt HSS