Button head screws have a large head that distributes weight over a larger area, increasing strength. Different types of screws have different recesses and threads for different materials. Coarse threads are used for softer materials like wood, while fine threads are used for metal. Self-tapping screws are used for thin sheet metal.
A button head screw has a swollen head that sits above the material held in place by the screw. The large underside of a button head screw distributes weight over a larger area than other types of screws, increasing the strength of the screw connection. Button head screws, including self-tapping machine, wood, and metal screws, can have a Phillips, slot, or hex recess to allow the screw to meet a variety of installation requirements. Proper selection of screw and head type requires knowledge of the base material holding the screw and the amount of pressure required to install the screw into the material.
Metal parts containing fine threads require button head cap screws with equally fine threads and a large diameter head to securely hold a material in a threaded hole while distributing force across the surface of the material. The distribution of pressure over a larger area prevents dimpling and tearing in the thin metals and other weak materials held in the connection. This increases the strength of a connection and adding a properly sized flat washer under the screw head will increase the holding force of the bolted connection. The threads of a machine screw are too fine to hold in softer materials such as wood and plastic. Another type of button head screw provides larger threads for softer materials.
The coarse threads of a button head wood screw grab and hold softer materials such as wood, plastics, and composite panels. Button head wood screws often have larger diameter heads than machine screws. This distributes the force of the connection over an even larger area than a soft material, avoiding indentations on the surface of the material or crushing surface fibers of softer woods such as pan head screws. Pine, plywood, and composite panels are all prone to surface damage from tapered screw heads. A third type of button head screw also has coarse threads, but is designed for a different type of material.
Sheet metal self-tapping screws often called Parker screws have coarse threads designed to tap into and hold in thin sheet metal. The button head of a self-tapping screw has a standard straight slot, but a Phillips head recess is common on smaller self-tapping screws. Installing a button head screw with self-tapping threads requires a lot of pressure, allowing the threads to cut through the sheet metal. Using this type of button head screw in other types of material will cause a weak connection which can break away from the base material under pressure.
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