Snap-on’s ½-inch-drive 12-piece semi-deep six-point metric impact socket set (312IMMS) ranges in sizes from 15 to 27 millimeters. The set features a flank drive wrenching system that grips the fastener on the flanks/flats to deliver more turning power, impact sockets that are heat-treated to a low hardness range to withstand the impact blows and wear rather than break, and a square drive-side hole that works with ball- or pin-type retention.