HRC 48-50 STEEL: Made of special steel with heat treatment, these drill bits have high hardness reaching HRC 48-50, elongated core and high concentricity for long-lasting use. 6 SLOT DIAMETER: With 6 pieces per pack, these saw drill bits have different diameters of 1/4 inch (6.4 mm), 5/16 inch (8 mm), 3/8 inch (9.5 mm), 1/2 inch (12.7 mm), 9/16 inch (14 mm) and 5/8 inch (16 mm). ASSORTED FOR DOUBLE EFFECT: They will achieve double effect by matching use with mortise and tenon machine, punching square holes needs to use electric drill, hammer and other tools. WIDELY APPLICABLE: They are a great accessory for mortising, chisel and working woodworking, suitable for construction, installation, renovation, decoration industry, etc. Product Description 6 Pcs Square Hole Drill Bits, Steel Hollow Chisel Woodworking Tools Set Professional drill bit, suitable for construction, installation, renovation, decoration industry, etc. 6 pieces per pack with different slot diameters to meet your needs.