Comes with 6, 9.5, and 12 mm (1/4, 3/8, and 1/2 in.) chucks to hold bits. Select a reversible model so you can back out bits or loosen screws. While a 12 mm (1/2 in.) drill can bore larger holes, a 9.5 mm (3/8 in.) variable speed reversible drill (upper left) can handle most home repairs.