Of all the tools in your tool box, the screwdriver will be the one most commonly used. Screwdrivers come in two basic versions.
Features of a Slotted Flat Blade Screwdriver
A "slotted flat blade screwdriver" is a long standard hand tool dating back to the 1500s. It has a flat bladed tip used to turn, fasten or loosen screws and bolts. The flat blade screwdriver is an extremely versatile tool and is used for fasteners of all sizes, providing significant leverage. Its disadvantage is that it is not self-centering in the fastener.
It has a handle for grip and comfort, a shaft and a head or blade at the end of the shaft. These last two items, blade width and shaft length, are the two measurements noted in a screwdriver size, for example 3/16 by 1-1/2. Unfortunately, the thickness of the flat blade is not given as a measurement and that is crucial for proper fit into the screw head slot.
A newer variation of the flat blade screwdriver uses a cross drive system and is commonly called a "phillips head screwdriver." These screwdrivers have a 123° point with a blunted tip and tapered cross-shaped blade tip that provides self centering on the screw and is designed to prevent over-tightening of the screw.
Although you may come across some other specialty screws in your home such as a square head screw, the slotted flat blade screw and screwdriver are the most commonly used tool (next to your long nose pliers or hammer).