A screwdriver is a tool used to apply rotational force to the heads of screws, to insert them or remove them from the hole that receives the screw. There are a wide range of screwdrivers, both due to the different shapes of screw heads that are intended to mate with the screwdriver's working end, and the need to have a wide range of screwdrivers for different conditions of working space, screw size, etc. While basic screwdrivers are hand tools, there are many power screwdrivers, driven by electric motors or compressed air. Even muscle-powered screwdrivers may have mechanical assists, such as ratchets or spring assists.
Screwdrivers are among the most universal tools, and among the most misused tools. While a screwdriver can be used as a chisel or pry bar, in such applications, it also can be a convenient way to damage the work or the worker.
Basic hand screwdriver
A typical screwdriver has a tip that mates to the screw head, a blade that connects it to a handle, and a handle used to apply the force. Blade lengths vary from "stubby", just enough to connect the handle and tip for tight working distances, to very long for reaching screws in awkward spots. Some blades may be flexibly jointed or made from springs so that the work can be approached from other than a perpendicular angle. An offset screwdriver has a right-angle bend just above the bit, and another just before the handle, so it can be used from the side of the work.
Some of the smallest screwdriver bits are on what are termed jeweller's screwdrivers. These are perhaps most often seen not for fine jewelry, but for fixing the tiny hinges on the frames of eyeglasses.