The Pro-Mix Screwdriver Bit Set includes 32 assorted 1 in (25 mm) long driver bits and one magnetic bit holder. 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 head profile is carefully controlled to ensure a tight fit significantly improving screwdriver bit performance.