8mm 10mm Shank Countersink Drill Bit Set Woodworking Cutter, Size: 2mm-7mm. Countersink Drill Bit Set 1PC/5PCS 1/4"(6.35mm) HEX Shank Woodworking Cutter. 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.