This Mortising Chisel is great Compatible With drilling square holes in wood with a mortising machine or a mortising attachment.Square hole drill can not be used on an electric drill, drill square holes need to fit a square hole drill drilling (mortise and tenon machine) to use.Mortise and tenon square hole drilled by the terrible + outer sleeve in the middle of the combination.Reduce labor intensity of construction workers, speed up the construction speed, reduce construction costs Compatible With construction, installation, renovation, decoration industries.Size: 1/4 inch (6.35mm), 5/16 inch (7.94mm), 3/8 inch (9.5mm), 1/2 inch (12.7mm)Material: high-speed steelHardness: HRC 48-50Color: silverClamping shank diameter: 19mm (Round) Length: 210mmPackage Contents:4 x Drill BitOnly the above package content, other products are not included.Note: Light shooting 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.