Phillips-head screws and screwdrivers were designed for power tools and assembly line usage, primarily for the automotive and appliance industries, though they have home uses as well. The curved, cross-shaped tip seats itself into the screw head and remains there while pressure and torque are applied. Once the screw is tightened, the tip is designed to slip out to prevent damage to the screw. The screwdrivers come in different sizes and types, depending on the job.
The shape of the Phillips screwdriver tip --- flat, oval or round for example --- varies depending on the type of screw it's used with. Phillips screwdriver tips will match up with the appropriate wood screws, machine screws or sheet metal screws. The wrong tip may not tighten the screw as easily or may damage the screw head.
Phillips screwdrivers come in five main types or styles. Most are straight blades with wooden or plastic handles. Ratchet screwdrivers with Phillips bits provide torque while removing the need to grip and regrip the handle. Multi-bit screwdrivers have interchangeable bits (i.e. flat, Phillips) with several sizes of Phillips tips included in the set. Offset Phillips screwdrivers are Z-shaped, with Phillips tips on both ends, for use in places where straight blade screwdrivers won't fit. Magnetized Phillips screwdrivers hold onto screws, recover dropped screws and prevent dropping screws in hard-to-reach places.
Blade lengths differ depending on the job. Long blades work best for screws that are difficult to get to, such as those deep in an engine compartment. Shorter blades work best for tight or close spaces.
Six Phillips screwdriver point sizes are available with an arbitrary numbering system. The point sizes correspond to the blade's diameter. Blade diameter and point size must match up with the screw head. Size zero matches up with diameter size zero. Size one goes with 3/16, 3 and 4 blade diameters. Blade diameters 1/4 and 6 to 10 fit the #2 point size. Diameters 5/16, 12 and 13 correspond to the #3 point size. Number 4 point size corresponds with 3/8, 20, 24 and 1/2 body diameters. A new size --- 00 --- is designed for use with small electronics.