A driver bit is an easily interchangeable part that snaps onto the screwdriver shaft to fit the head of the screw. Depending on the type of screw, the tip can be flat, rounded or Philips... Screwdriver bits are usually made of steel, chrome vanadium or titanium. Steel tips are cheaper, but they can damage the screw head if not aligned precisely. Chrome vanadium tips are more expensive but more resistant to damage and titanium is the most expensive but also the most durable.