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 2mm, 2.5mm, 3mm, 4mm, 5mm and 6mm Bit Sockets6 Piece 1/4" Drive Metric Hex Bit Socket Set includes 2mm, 2.5mm, 3mm, 4mm, 5mm and 6mm Bit Sockets packaged on a clip rail.