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 4mm, 5mm, and 6mm Slotted; #1, #2, #3 Phillips; and #2 POZIDRIV Bit Sockets7 Piece Screwdriver Bit Socket Set includes: 4mm, 5mm, and 6mm Slotted; #1, #2, #3 Phillips; and #2 POZIDRIV Bit Sockets packaged on a clip rail.