Delta 5/16" x 5/16" Professional Mortising Chisel 17-785 Product Dimensions: 8.3×1.2×1.2 inches Constructed of high quality steel for sharpness and durability Center drill bit removes material, hollow chisel squares off the sides Drills 5/16-inch square holes for making mortise and tenon joints Fits Delta mortising attachments, mortising machines, and boring machines 2-piece design for easy re-sharpening