A Guide to Screw Types
In the fittings industry we often talk about products and their uses with the assumption that customers know exactly what they are and what they do, but with DIY being ever more popular we thought it might be a good idea to provide a basic rundown of some of the more common types of screws and their uses to help out the DIY amateurs out there.
The head of a screw serves to house the drive type of the screw as well as providing a stopping point once the screw has been driven into a surface, thus allowing you to remove the screw if needed. The major differences between head types are the space they take up in regards to precision jobs, as well as whether the head is countersunk or not, countersunk heads being those that have tapered undersides that are used to allow the head of the screw to sit deeper into the surface and not protrude, providing a flatter overall surface.
Pan: Pan heads are one of the most common head types; they are slightly rounded and have short vertical sides to provide a relatively low profile once driven into a surface.
Flat: Flat heads are predominantly countersunk and are designed to sit low in the surface that the screw has been drilled into; removing any awkward protrusions that could interfere with further work on the final product.
Oval: Oval heads provide a combination of pan and flat head types, with the actual head being slightly rounded while retaining a countersunk underside; they are primarily used when a decorative finish is needed due to the aesthetic effects that they provide.
Truss: Truss heads have a rounded top with a large, flat underside that provides an ultra-low profile while still being above the line of the surface.
Screw threads are the combination of ridges and recesses on the body of the screw that allow for the screw to be fixed into place via a compatible thread inside of a pre drilled hole or nut, the exterior threads on screws are thus known as “male” while the interior threads of their intended location are “female”.
Machine Screw Threads: Machine threads are the standard thread type, designed to fit with a pre-drilled interior thread of a nut or tapped hole, they have few unique features aside from a high degree of accuracy when it comes into screwing into their intended partner thread.
Wood Screw Threads: Wood screw threads are specifically designed for use in wood; they have a sharp, tapered point and wide threads to allow them to be drilled into a wooden surface directly rather than requiring a pre-drilled hole to fit into.
Sheet Metal Threads: Sheet metal threads feature particularly sharp threads to help attach to metals and often feature a tapered point in the same manner as wood screws to allow them to be drilled into the surface directly.
Self-tapping: Self-tapping screws are machine threaded style screws that feature the sharp tapered point of screws like the wood and sheet metal varieties discusses above, thus allowing them to be drilled directly into a surface or to correct for any inaccuracies in a pre-drilled partner hole.
The drive type of a screw essentially determines which sort of screwdriver that you’ll need to use to fasten the screw, while some screwdrivers can be used for multiple types of screws most drives require a specific screwdriver type.
Slotted: Slotted drives are a traditional but still popular style that employs a simple, single slot for a flat-tip screwdriver. It offers few special properties aside from its simple design and ease of use.
Phillips: A Phillips drive has a cruciform shape and is designed to work with a Phillips screwdriver, the main advantages of this type of screw are that the extra traction of multiple edges reduces the amount of force required by the user, as well as being designed to cause the screwdriver to pop out of the head recess when subject to a high degree of force in order to prevent damage to the screw threads, the downside however is that this often causes the screwdriver to cause damage to the head recess itself.
Pozi: Pozidrive screws are a further development of the Phillips drive and features two cruciform slots, with the second being less pronounced than the standard cross drive. This type of drive offers additional stability and reduces the built-in slippage of the original Phillips drive. While still being compatible with the standard Phillips screwdriver, it is recommended to use a specific Pozidrive screwdriver to avoid damage to the head.
Square: While not as common as the standard slot and Phillips drives, square screw drives enjoy popularity in Canada and a number of other countries. The simple shape of the square drive allows a square screwdriver to be inserted and twisted easily without having to worry about positioning to ensure precision threading. The spread out contact area however is not useful for transferring a high degree of force if needed.
Hex Socket: Hex socket drives feature a hexagonal recess and are driven with the use of a hex key or hex screwdriver, the main benefit of this type of drive is the high number of contact surfaces reduce the amount of force required to turn the screw while also helping to reduce slippage and thus damage to the screw, the downside being that the amount of force that can be used with this drive type is limited much like the square drive socket.
Star: Star drives or “Torx” drives have a star shaped recess with six rounded points. It’s primary benefits are a reduction in the amount of force required to turn the screw as well as effectively eliminating slippage while maintaining the longevity of the screw and the driver used, which is a specialist Torx screwdriver. There are also a variety of tamper-resistant star drive types that include pins in the centre of the main recess that require a highly specialised tool to turn.
In need of screws?
We stock a wide variety of useful screw types on our online store over at the Screws & Fittings section.