A screwdriver is a
tool, manual or powered, for screwing and unscrewing (inserting and removing)
screws. A typical simple screwdriver has a handle and a shaft, ending in a tip
the user puts into the screw head before turning the handle. 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—or ridged or treated for additional 'grip'. Handles are typically wood, metal,
or plastic and 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 that fit into a socket on
the end of the shaft and are held in mechanically or magnetically. These often
have a hollow handle that contains various types and sizes of tips, and a
reversible ratchet action that allows multiple full turns without repositioning
the tip or the user's hand.
A screwdriver is classified by its tip, which is
shaped to fit the driving surfaces—slots, grooves, recesses, etc.—on the
corresponding screw head. Proper use requires that the screwdriver's tip engage
the head of a screw of the same size and type designation as the screwdriver
tip. Screwdriver tips are available in a wide variety of types and sizes (List
of screw drives). The two most
common are the simple 'blade'-type for slotted screws, and Phillips,
generically called "cross-recess".
The handle and
shaft of screwdrivers have changed considerably over time. The design is
influenced by both purpose and manufacturing requirements. It has a handle because
it to be easy to wind.
The shape
and material of many modern screwdriver handles are designed to fit comfortably
in the user's hand, for user comfort and to facilitate maximum control and
torque. Designs include indentations for the user's fingers, and surfaces of a
soft material such as thermoplastic elastomer to increase comfort and grip.
Composite handles of rigid plastic and rubber are also common. Many screwdriver handles are not
smooth and often not round, but have flats or other irregularities to
improve grip and to prevent the tool from rolling when on a flat surface.
