4-Piece Woodworking Mortising Chisel Set Bit 1/4-to-1/2-Inch 6-12.7mm This Mortising Chisel set is great for drilling square holes in wood with a mortising machine Fits mortising attachments with 3/4" collars Material: high-speed steel, Hardness: 56HRC Set of 4 - 1/4-Inch(6mm), 5/16-Inch(8mm), 3/8-Inch(10mm) and 1/2-Inch(12.7mm) Use matters: Square hole drill is mainly used for woodworking aspects.