[Square Hole Size]: 1/4 inch / 6.4mm, 5/16 inch / 8mm, 3/8 inch / 9.5mm, 1/2 inch / 12.7mm. Refers to the length of the edge of the square hole drilled with the square drill. [Application]: This mortising chisel is ideal for drilling square holes in wood with a mortising machine or mortising attachment. Suitable for use in woodworking, construction, installation and decoration industries. [Features]: Reduce the labor intensity of construction workers, speed up the construction speed. [Material]: high strength and hardness, made of high quality material, wear-resistant and easy to use. [Note]: Other dimensions are shown in the picture. Please avoid 1-2mm error due to manual measurement. Product Description Item Descriptions: -[Square Hole Size]: 1/4 inch / 6.4mm, 5/16 inch / 8mm, 3/8 inch / 9.5mm, 1/2 inch / 12.7mm. Refers to the length of the edge of the square hole drilled by the square drill. -[Application]: This mortising chisel is ideal for drilling square holes in wood using a