UN100-021 | Holemaker Bi-Metal Holesaw 21mm Dia.PREMIUM QUALITY BI-METAL M42 COBALT HIGH SPEED STEEL. Suitable for drilling a wide range of materials including steel aluminium brass cast iron plastics & wood. The M42(8% Cobalt) high speed steel teeth offer optimal cutting life & performance.VARIABLE PITCH 4 / 6 TEETH PER INCH. For reduced vibration delivering increased life performance & accuracy.Diameter: 21mm (13/16 ), Thread: 1/2