PTI PH2 x 150mm Extra Hard 1/4" Hex Screwdriver Bit Screwdriver bits are typically made up of a shaft and a tip. A screwdriver bit's shaft is typically hexagonal in shape, with six flat sides. This shaft is fitted into the end of a screwdriver that has a bit holder. The shaft's shape prevents the bit from rotating within the bit holder. The tip end of a screwdriver bit may have many shapes.The bit's head is designed to fit into the head of a screw. As the screwdriver is spun, the bit rotates as well. This is what causes the screw to turn. Head style: Phillips Length: 150mm Henry F. Phillips intentionally designed the Phillips screw driver to cam out when the screw stalled in order to prevent the fastener from damaging the work or the head and instead damaging the driver. Philips bits resemble a cross and are available in a variety of sizes. Extra hard bits are suitable for soft fixing. Ie. screwing into wood and high wear applications.