The Irwin 4X Blue Groove Flat Bits have a patented groove point, and cutting edge designed to cut and not scrape the timber 4 times faster than standard flat bits. The parabolic scoop optimises control and removal of wood chips. Increased relief angle from 12° to 17°. The shank is 157mm in length and 10% larger in diameter for added durability.The Irwin IRW10506629 8 piece Blue Groove 4X flat bit set includes the following pieces:12, 16, 18, 20, 22, 25, 28 and 32mm diameter bits.