The Mibro CRV Screwdriver Bit Set includes 36 assorted driver bits, three non-magnetic nut setters and one magnetic bit holder for 1 in. (25.4 mm) screwdriver bits. The driver bits are manufactured with S2 chrome molybdenum steel to offer a consistent Rockwell hardness (HRC) of 59-61, which ensures the bit tips are hard enough to keep their shape but not too hard to damage the screw head. The screwdriver bit head profile is carefully controlled to ensure a tight fit, significantly improving screwdriver bit performance.