The Surface Drive design prevents rounding of fasteners, and these wrenches can be used along any length of a threaded rod without having to move the wrench from the fastener. Combination ratcheting wrench sizes: 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 and 24 mm.