A screw may be defined as an inclined plane wrapped around a nail and characterized by a helical ridge. In other words, it is a long metal shaft with threads circling along its length. It also has a turning where a screwdriver can be used to rotate the screw. A screw generally has a head with a specially formed shape. The shape determines and heads size the size of the tool to be used to turn or drive the screw. Commonly used tools are wrenches and screwdrivers.