Screwdrivers come in many different lengths, handle types and tip shapes. The most important part to get right is the screwdriver tip shape as using the incorrect fitment can easily damage the screw head, this can be a nightmare and will take a lot longer to get out so its worth making sure the screw head matches the type of screwdriver.
Most common screwdriver tip types:
Slotted – Slotted screwdrivers are the most basic type, they consist of a straight tip that slots into a groove in the fasteners head. The tip of the screwdriver tapers down to make locating it in the slot easier. The straight tip allows a large contact area however the grooves are usual quite shallow meaning it can be easy to damage the tool or the screw if too much force is applied or if the screw head is rusty. Using the correct size tip for the groove is the best way to avoid this. For example a tip that is too small for the groove will only contact on 2 points when pressure is applied meaning damage is more likely.
Another common issue with slotted screwdrivers is that when you are turning the tool the tip of the screwdriver works its way along the groove then falls out, this is because there in nothing stopping the tool at the end of the grooves. This isn’t too much of an issue when using it by hand but it makes using an electric screwdriver very difficult with slotted screwdriver attachments due to the speed it is spinning. This isn’t a problem with Philips are Pozi-drive.
Philips – A Philips type drive is a cross shaped head that is usually tapered or domed towards the end of the tip to allow easier location into the screw, the domed tip means there is less chance of incorrectly positioning the head and causing damage.
The only time a tapered or domed head isn’t as beneficial is when the screw is very tight and requires extra force to loosen, this is because there is less contact with the screw faces and the sloped taper can encourage the screwdriver to disengage.
Pozi – A Posi-drive screwdriver is an improvement on the Philips, where the Philip has 1 cross the Pozi-Drive has a double cross pattern at a 45 degree to the first cross. This design allows for many more contact points between the driver and the screw head. The benefit of this is there is much less chance of slipping under high torque. For this reason, you also stand a higher chance of removing a rusty fastener with a Pozi then a Philips.
Hex – A Hex or Allen screwdriver is a very popular fastener type, they are commonly used in automotive and home furniture. As the name suggests the tool features a hexagon shaped drive. Hex drive fasteners are more commonly used for bolts as opposed to screws.
Due to the deep recessed hexagon in the bolt with flat sides and lots of contact points it’s unlikely that the tool will slip. This makes for an ideal fastener for when the bolt needs to be tighter than a screw with a Pozi or Philips head. It is often used with an electric/battery screwdriver as it can withstand the torque easily.
The only time you may have an issue is if the bolt head is rusty and the deep hexagon shaped hole is corroded. It may be worth gently tapping the tool to ensure the tool is all the way in the fastener as you will run the risk of rounding it if the tool is only partially located due to the rust.
Torx – Torx screwdrivers are the shape of a star, they are similar to hex drive screwdrivers as they fit into a deep recess in the screw or bolt head. They can take more torque without rounding or damaging the fastener than a hex drive thanks to the points on the star shape being far more prominent than the ends of the flats on the hex.
Like the hex drive the only time you may have an issue with the tool slipping is if the screw or bolt head is corroded, if the tool isn’t all the way in due to rust inside the torx whole it can be quite easy to round the fastener. If the screw or bolt head is very corroded it can make the prongs of the star weak but usually by making sure the tool is properly located you can still undo the fastener.
Less Common Tip Types
Tamperproof Torx – A tamperproof torx screwdriver also known as a security torx is the same as a normal torx or star drive however the centre of the tool is hollow, the corresponding tamperproof bolt or screw has a solid centre that the hollow of the tool slides over. As the name suggests the tool is designed to undo fasteners that are not designed to be undone by someone accidently with a regular Torx, This may be to prevent damage to a component that requires extra care when working on. Tamperproof Torx are often found within the automotive industry, especially more delicate electrical components like engine ECU’s that could be easily damaged if it is opened up by someone without training.
Tamperproof Hex – A tamperproof hex has the same purpose as a tamperproof Torx, the hollow hole in the centre of the Torx fits over the raised centre on the fastener where a regular hex tip wouldn’t be able to. Just like the tamperproof Torx these are to stop untrained people accessing components that may be easily damaged. Tamperproof Hex fasteners are less common that Torx but they are mainly found in the automotive industry.
Square – The use of square drive fasteners has decreased in use over the last 10 years, square drive can still be found in some construction and timber work, but it has been widely replaced by the Hex Drive fasteners. As the name suggests the tip of the tool is square with a slight taper inward to allow a positive connection with the corresponding fastener. The square drive can withstand a high amount of torque thanks to the deep flat sides, for this reason they are more commonly found in bolt form. The Hex drive is an improvement over the square, the hexagon shape allows more contact points while still utilising the deep flat sides.
Clutch – A Clutch or Slotted Tamperproof One Way type fastener is designed to be tightened in one direction with a normal slotted screwdriver, once tightened its impossible to undo with the same screwdriver as it is designed to slip when torque is applied in the opposite direction, It is often used as more of a rivet than a screw as it’s a permanent fixing that requires drilling out to remove. To get over the need to drill the fastener, a comprehensive screwdriver bit set will come with a bow tie shaped bit that will undo the fastener.
Spline – A Spline tip screwdriver is often known as a 12 point or multipoint, It is effectively a double Torx with 12 points, the points are shorter than the points on a Torx but as there are so many contact points they rarely slip or round under load, making them ideal for larger bolts. Spline Fasteners are commonly used in automotive suspension.
Spanner – This is a type of security screw head, the tip of the tool looks like a spanner hence the name. The 2 points of the tool slot into the fixing to drive the screw, the points on the end of the tool are quite thin and fragile so you will usual find these fasteners on screws rather than bolts that require a high torque. It would be quite easy to break the 2 pins under heavy load. The reason they are classed as security fasteners is because it is very hard to insert another incorrect tip type or other driver into the head of the screw, this makes them ideal for applications in prisons or schools.
Schrader – Schrader Screwdrivers/Keys have a specific purpose, they are designed to remove the core from Schrader valves, these are the valves that allow you to pump up your car, motorcycle or bicycles tyres. These valves operate when the centre is pushed down via the pump to allow the air in or out of the tyre through the valve. The core of the valve is threaded, the purpose of the Schrader key or screwdriver is to unscrew/screw the valve core. The is needed for tyre replacement to let the air out of the tyre faster or commonly to replace the core due to the airtight seal leaking.
The other place Schrader valves are used is on vehicle air conditioning systems. They are used for the same reason as tyre valves, to create an airtight seal and allow Air Con gas to be removed or added to the system. The Valve Key would be used to remove the valve to replace a leaking core. Schrader valve keys don’t usually come as part of a screwdriver bit set, they are usually on a fixed small screwdriver.