Professional design, ideal for drilling square holes in wood with a mortiser. Fits all machines and drill bits. Square hole drill bits are mainly used in woodworking. Material and Size: Made of high speed steel. Heat treatment, HRC48~50, high hardness, extended center, high concentricity; 4 sizes: 1/4 inch (6.35mm), 5/16 inch (7.94mm), 3/8 inch (9.5mm), 1/2 inch (12.7mm). Why choose this item: Reduces the labor intensity of construction workers, accelerates the working speed and reduces costs. Perfect for construction, renovation and decoration. Package includes: 1 piece 1/4" (6.35mm), 1 piece 5/16" (7.94mm), 1 piece 3/8" (9.5mm), 1 piece 1/2 inch (12.7mm), Note: The punch square must be made with a drill, hammer or other tools. (None of these items are included in the delivery). Note: The data is all measured manually, please allow 1-3 cm error due to the difference in light and display, there may be color differences, please refer to the actual item received.