4 different sizes: 6.4mm, 8mm, 9.5mm, 12.7mm. Made of high-speed steel, high hardness, durable and practical, heat treated, long service life. Square hole drills cannot be used on electric drills. Square hole drills need to be used with square hole drills (tenon and groove machines). Fits all mortise and drill attachments. Square hole drills are mainly used in woodworking. Reduce the labor intensity of construction personnel, speed up the construction speed, and reduce the construction cost of construction, installation, decoration, and decoration industries. Protection design: The design of the ferrule drill sleeve can effectively protect against explosion in the initial stage of use. Sizes - 4 sizes in total including 6mm / 8mm / 10mm / 12.5mm. This mortise chisel set is a must-have for home woodworking. Features: Material: High Speed Steel. Color: Silver. Dimensions: 6.4mm/8mm/9.5mm/12.7mm. Contents: 1x 6.4mm square hole drill. 1 x 8mm square hole drill. 1 x 9.5mm square hole drill. 1 x 12.7mm square hole drill.