A screwdriver is a tool, manual or powered, for turning (driving or removing) screws. A typical simple screwdriver has a handle, a shaft, and a tip which is inserted into the head of the screw to turn it. The shaft is usually made of tough steel to resist bending or twisting. The tip may be hardened to resist wear; treated with a dark tip coating for improved visual contrast between tip and screw, and/or ridged or treated for additional 'grip'. The handle can be wood, metal, or plastic and is usually hexagonal, square, or oval in cross-section to improve grip and prevent the tool from rolling when set down. Some manual screwdrivers have interchangeable tips which fit into a socket on the end of the shaft and held in magnetically. These often have a hollow handle containing a set of tips of various types and sizes, and a reversible ratchet action, much like a socket wrench, allowing multiple full turns without repositioning either the tip or the user's hand.