A single-size tool beats an adjustable tool hands-down most of the time — but that doesn’t mean there’s no place for the adjustable tool. For instance, if you owned this $30 adjustable bit from Irwin, you could save yourself some money by just buying the sizes you need and using this one for those rare times you need another odd size.
Irwin’s adjustable wood bit can cut holes in 1/8″ increments from 7/8″ to 3″. You attach one cutter to bore holes from 7/8″ to 1-3/4″ and the other cutter for holes from 1-3/4″ to 3″. Simply loosen the lockhead screw to adjust your hole size or change cutters.
With its slow-feed screw point, the 6-1/2″-long drop-forged bit powers through most types of wood. Irwin designed the 11/32″ shank with three equally spaced flats to line up with three-jawed chucks.
Be careful if you buy this product from Amazon — they seem to have mixed this product up with another one. They picture the bit with three cutters instead of two, and they also make the same mistake at one point in their writeup.