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: Robertson Square R1 Length: 90mm PTI R1 x 90mm Screwdriver Bit 1/4" Hex P.L. Robertson, a Canadian, created square recess bits, commonly known as Robertson bits, in 1908. The head features a little taper, which makes it much simpler to insert the bit and hold the screw on the bit. If you want to prevent cam-out, they are far more reliable than Phillips and slotted bits, however hex bits are gradually displacing them in current times. There are three sizes of these bits: #1, #2, and #3.