HRC 48-50 STEEL: Made of special heat-treated steel, these drill bits have a high hardness of HRC 48-50, an elongated core, and high concentricity for long-lasting use. 6 SLOT DIAMETERS: With 6 pieces per pack, these saw drill bits have different diameters: 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). DUAL EFFECT SET: They achieve a dual effect when used in combination with a mortise and tenon machine. Punching square holes requires an electric drill, hammer, and other tools. WIDELY APPLICABLE: They are an excellent accessory for mortising, chiseling, and woodworking. Suitable for construction, installation, renovation, the decoration industry, etc.