Guide to Screw Elements
There are a number of elements that can differentiate types of screws from one another, and make them more suitable for certain applications and materials.
We’ve put together the ultimate guide to screw types to help you decide which might be right for you.
Recess Style
The recess refers to the indentations on the screw head that form particular shapes. These will often have an accompanying screwdriver to use solely with each head. Some of the most common forms are:
Slotted – a single line indentation across the head of the screw.
Phillips Recess – a cross recess in the shape of a ‘+’. Often used for self-drilling, drywall and window screws.
Pozi/Cross Recess – similar to the Phillips recess, but with fur extra contact points in between the main lines of the cross shape. Phillips and Pozi screws are difficult to tell from far apart, but on closer inspection you’ll be able to see the extra lines. These screws are commonly used in woodscrews and chipboard screws.
Combi Recess – a combination between the traditional slotted and Pozi styles for extra hold.
Square Recess/Robertson Drive – a square shaped indent on the screw head. Often used for square drive pan self drilling and solo screws.
Head Types
The screw head is the part of the screw the screwdriver will fit into when driving the screw into a surface. They will slot into the recess, which is located on the head.
Countersunk Head – specifically designed for sinking into timber and giving a flush finish.
Double Countersunk – an improved design of the countersunk, with additional head strength to assist countersinking.
Double Countersunk with Ribs – ribs under the head further assist with the countersinking process.
Wafer/Flange/Pancake – a lower profile head with flatter underside. This is better to use when a large clamping area and obstructive head is required.
Pan/Round Head – a screw head with a flat underside designed for fixing against metal surfaces primarily.
Hexagon Head – these screws include an integral washer to help the effectiveness of the clamping.
Bugle Head – these screws have curved surfaces under the head to prevent damage and tearing to plasterboard paper, where they are most commonly used.
Socket Button Head – these screws are designed with a raised finish and a flat underside to aid clamping.
Socket Cap Head – a very common industry standard screw with a hex head, requiring a key to loosen or tighten.
Thread Types
The screw thread is the helical shaped ridge wrapped around the screw, creating the driving force to help sink into different materials.
Self Tapping Thread – a common, neat thread design mainly used in steel applications where the screw can tap it’s own hole as it is drilled into materials.
Twin Thread – threads designed to give a fast insertion time in softer materials.
Coarse Thread – wider threads, often referred to as spaced threads, that are often used on screws for timber applications.
Fine Thread – also known as metric threads, these threads are used mainly with steel applications and are places closer to the body of the screw than other threads.
Serrated Thread – this thread type reduces the torque required to install the fastener as well as assisting with the speed of insertion.
Hi-Lo Thread – these threads have superior holding power and are often used in soft timbers and thin sheets.
Point Style
The point style, as the name might suggest, is the style of the point at the end of the screw. Some points are sharper to drive into harder materials.
AB Point – this is a sharp pointed screw used for pre-drilled sheet material applications.
Needle/Gimlet/Super Sharp Point – these screw heads are designed for piercing timber, plastic and other light materials without predrilling being necessary.
B Point – these are flat point screws to be used in pre drilled shallow holes.
Self Drill Point – these screws are designed for drilling into metals without the need for pre drilling.
C2 Slash – these sharp point screws are twin cut to allow for rapid pick up and are known to reduce splitting.
Type 17 Point – also known as slash point screws, they are used for flashing timber without the need for pre drilling, and again help reduce splitting of the timber.
Finishes
This refers to the metal the screw is made from, or the ‘plating’ – the outer wrap of metal – that the screw is finished in. Each finish has different benefits and is more suitable for certain materials and uses.
Bright – this is a polished only finished screw.
Zinc – a bright zinc electrolytic plating that is toxin free. They are very resistant to corrosion to are suitable for the majority of indoor and outdoor industrial applications.
Black Phosphate – this is a very rust resistant screw, the phosphate is meant to keep wet drywall compounds from causing screw heads to rust.
Nickel – nickel is also corrosion resistant, but it boasts superior strength and resistance to further wear.
Galvanised – galvanised steel is lower cost than stainless, however it has a very long life expectancy. It’s very resistant to mechanical damage.
BZP – bright zinc plated finishes are where standard steel is coated with a thin layer of zinc. This coating is incredibly resistant to rusting and oxidisation.
YBZP – yellow bright zinc plating boasts many of the same benefits as BZP, and the addition of the yellow not only adds a iridescent finish but adds extra strength.