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: Hex 5/64" Length: 25mm PTI 5/64" x 25mm 1/4" Hex Socket Head Bit These hex bits, which are essentially an allen key that you can insert into your drill, are frequently used while assembling do-it-yourself furniture and for situations where allen key access is restricted by nearby obstructions. The majority of hex-drive screws have a 5mm standard size.