Widely Used-Great for drilling square holes in wood with a mortising machine or a mortising attachment. Easy to Use-It will get double effect by matched use with mortise and tenon machine.The square hole punching needs to use electric drill, hammer or other tools. Save Time-these woodworking morstising chisel bits can reduce labor intensity of construction workers, the construction speed, reduce construction costs for construction, installation, renovation, decoration industrie. High Quality-these square hole drill bits made of metal, through heat processing, with high hardness drill bits, and -edged square chisel, . Dimensions: 6.4mm aperture (165mm total length), 8mm aperture (205mm total length), 9.5mm aperture (205mm total length), 12.7mm aperture (210mm total length) Material:metal colour:Silver Package Contents: 4 x Square hole drill Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.