Traditionally, the most common form of screwdriver is the fixed blade, in either a flat or Phillips head. Now, with new applications continually emerging, there are over a dozen types of screw-heads, but essentially three types of screwdrivers--the original fixed blade, and two types with interchangeable heads.
The fixed-blade screwdriver consist of a one-piece metal shaft with a moulded handle, usually made from plastic or wood. The tip of a fixed blade is always formed to fit the head of specific type, and size range, of screw. The advantage of fixed blades is that they are one solid piece, making them the quickest to use, and they are generally the choice for small, precision jobs. The drawback with fixed blades is that you will need a different screwdriver for different types and sizes of screws, such as a flat, Phillips or star head screws.
Standard Interchangeable Bit Screwdrivers
Interchangeable bit screwdrivers are the most versatile as they have a single shaft and handle assembly that will accept an unlimited number of heads, or bits, for different types of screws. Drivers can be either fixed position, like a fixed blade, where you have to continually remove and reinsert the screwdriver tip into the screw, or ratchet style. The advantage of interchangeable bits is that you can start small with a basic kit and then add bits when needed. The drawback is that the bits are easily misplaced.
Power screwdrivers also accept interchangeable bits and come in different forms. Most power screwdrivers are electric, but there are also pneumonic, or air powered, versions. Most power screwdriver are cordless and look like drills, but generally will have specific features such as reverse direction, adjustable torque settings and internal clutches to prevent too much force from being applied. There are also smaller power screwdriver that look similar to a fixed blade. The advantages of power screwdrivers is that they can install or remove screws with a minimal amount of effort and can also be used with extensions and right-angled attachments. The drawback with power screwdrivers is that they can be too powerful and strip the screw's head in a fraction of second, if used improperly.