CSLU-Tool Woodworker 5/8"(16mm) Square Hole Drill Bits Mortising Chisel Set, Mortise Chisel & Bit Set Fits all mortising machines and drill press attachments 1/4-Inch, 5/16-Inch, 3/8-Inch, 9/16-Inch, 5/8-Inch and 1/2-Inch sizes Made of the highest quality tool steel High performance flute design geometry for superior chip extraction Hardness: HRC 48~50