Popular Screw Heads
The two most common screw heads are the slotted screw drive and the Phillips head. Slotted features a single indentation for use with a standard screwdriver. Once the only game in town, the slotted screw’s use has declined since the rise in popularity of the Phillips screw in the 1930's. The Phillips-head, otherwise known as the crosshead, features two slots in an "X" pattern. The advantage of the Phillips head is increased torque, which allows more energy to transfer to the screw, helping it penetrate a surface. Far more secure when being tightened, the Phillip’s head is also safer to the user as the driver is less likely to slip out of the screw when being tightened.
While the head of a screw can help grip the driver, helping the screw penetrate the surface, the body of the screw is specially designed for maximum efficiency. Broken into several categories, using the right screw will assure best results and save time. Some of the more popular categories are wood screws, machine screws, thread-cutting machine screws, sheet metal screw, self-drilling screws and socket screws.
Common Screw Head Surfaces
While the slotting of a screw helps determine what the screw can be used for, so too does the surface. Most common screws have flat-heads causing them to sit flush to the surface when tightened. Primarily used for wood, flat-heads can have either a single slot or Phillips slot. A pan head has a larger diameter than most screws with a high outer edge and is useful when high tightening is needed. Round head screws can still be found in workshop junk drawers but are rapidly becoming a less common design. Dome-shaped with a single slot or Phillips slot, the round head tends to stick out of the surface making it hard to hide. Oval head screws tend to be used ornamentally. Often called oval countersunk, it is similar to a flat-head but has a slight rounded surface. This screw is common on light switch and electrical outlet plates.
Less Common Screw Head Surfaces
A little less common, but very useful, are the slotted hex, truss, socket and button-head screws. Slotted hex features a bolt like surface with a built in washer and a slot for the driver. Useful in mounting, the screw can be turned by a screwdriver or a wrench. The truss head has an extra wide surface with a rounded top. Usually featuring a Phillips slot, the truss offers better surface grip and security. A socket head screw is designed with a socket recession to accommodate a socket driver as does a button head screw. The difference between the two is the socket cap has a cylindrical raised head and the button has a slightly domed surface.