Patented bit holding system forces bit surface to opposing side for maximum bit retention, strength. Packaged in patented impact resistant "slide rail" system . Heat treated socket bases for durability and service ability. Chrome sockets, S2 and alloy steel bits. Includes 6mm, 8mm, 10mm, and 12mm Bit Sockets4 Piece 3/8" Triple Square Metric Bit Socket Set includes: 6mm, 8mm, 10mm, and 12mm Bit Sockets packaged on a clip rail.