Screws are a type of threaded fastener used to join objects and hold them together. A screw consists of a head and threaded section which, depending on the design, may or may not flush out with the surface during fastening. There are many different types of screw heads including flat head, round head, raised head, truss head, bugle head, and more, each designed and used for a specific purpose. This blog will cover the many types of screw heads and their unique characteristics.
In their most basic form, screws are divided into two groups: countersunk screw heads and non-countersunk screw heads. In a countersunk screw head, there is an angular shape beneath the beneath the head, while in non-countersunk screw heads, there is a flat shape. To create the countersunk head, a countersink bit is drilled into the screw to provide the correct head angle. In non-countersunk screw heads, there is no pre-drilled hole necessary. In each group, there are many further classifications. Countersunk screw heads include flat heads, oval heads, and bugle heads, while examples of non-countersunk screw heads are pan heads, button heads, round heads, binding heads, flange heads, and socket heads.
Countersunk Screw Heads
The first type of countersunk screw head, the flat head, sits entirely in the same plane of the mating surface. These screw heads feature a flat top surface and a cone under the bearing surface with a standard of 82 degrees. These are ideal for use in areas where protrusion is unacceptable, such as in a bookshelf. Other applications of flat head screws include steel applications and door hinges. Oval heads are the same as flat heads but feature a dome-shaped head rather than a flat top, making them slightly more aesthetically pleasing without affecting performance. Finally, bugle heads have a flat top surface and a concave curve shape below the bearing to reduce surface damage. These heads are capable of distributing bearing stress over a wider area and are most commonly used in drywall.
Non-countersunk Screw Heads
Pan heads are the first type of non-countersunk screw heads. These feature a flat or slightly round head with chamfered edges and a flat load-bearing surface on the underside. Pan heads have moderate head height and diameter and provide high tightening torques. Button heads are domed, large diameter heads with high resistance to slipping and stripping. These are ideal for lighter fastening operations and will not be suitable for high strength applications. Round screw heads have a high profile and deep drive cut, but a smaller diameter. These were once the most popular types of screw heads but many now consider them outdated.
Binding heads are similar to pan heads, but feature a much thicker bearing surface and deeper slot, both of which increase the screw’s bearing capacity. A flange head can be considered a combination of a screw and washer. The head can be circular or hexagonal with a washer underneath the load bearing surface. This distributes pressure to help keep the screw in position and increase its bearing capacity. Finally, socket heads are the strongest type of screw head. Known for their quality and reliability, they are made from high grade carbon and stainless steel. Screw heads of this type feature a cylindrical head and long vertical sides. Their head height and shank diameters are equal, allowing them to be used in very high-strength endurance applications.
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