Irwin 49909 9/16" X 7-1/2" Dual Auger Wood Boring Bits Solid center design provides extra rigidity while boring Wide lands keep the bit straight as it bores through the hole Single-spur cutting edge scribes the circumference of the hole for a smoother finish Fast boring in hard and soft woods. Bits have a 4-1/2" twist length and a 7-1/2" overall length Full-length heat treatment guards against bending and strengthens the twist