Types Of Screw Heads

A Simple Guide to Choosing the Right Screwdriver Bit

Most of us simply think of screwdrivers as being either slotted or Phillips. In truth, there are many other types you may not be aware of.

That is, at least, until you suddenly find yourself trying to fix the washing machine, only to find some strange screw head you have never seen before.

There are more than a dozen different types of screw head in use today. This guide is designed to help you find the right screwdriver for each application.

Table of contents

Slottedslotted bit

This is the first known screw style, and even today you can still find it in use practically everywhere. The problem with these is that far too often, the screwdriver slips out of the slot or damages the slot if you are using too much force. Slotted screw heads come in a range of sizes, the most common of which are #1, #2, and #3.

Phillips

The Phillips drive has become one of the most popular screw heads in the world. The design allows you to apply more force without having to worry about stripping the head. These screws come in a range of drive sizes, the most common of which are #1, #2, and #3; of these, the #2 size is the most commonly used.

Tamper-Resistant Phillips

These are relatively uncommon and are typically used by manufacturers in their tools or products to keep consumers from tampering with or attempting to modify them. They look just like the standard Phillips drive, but there is a tamper-resistant pin located in the middle of the cross. These screws are not used in applications where high levels of torque are applied, as the head design is quite weak.

Pozidriv®

We don’t see a lot of these here in the U.S., but they are very common in Europe. They look a lot like a standard Phillips drive but there are four additional contact points, designed to reduce the risk of damage under high torque. They were originally designed for use with power screwdrivers.

Quadrex

This screw head looks like a combination Phillips and square recess drive. You see a lot of these being used in electronics and appliances built in China. While it looks like you should be able to use either a Phillips or square drive, you must have the right bit or you will strip the head.

Square Recess

These screws are becoming very popular, as they have a high resistance to “camming out”. Camming occurs when the screwdriver tip slips out of the head and damages it to the point at which the head is stripped out. The most common sizes in use today are #1 and #2, but you may find others depending on the application. This type of drive is also referred to “Robertson.” It is not made for high-torque applications.

Tamper-Resistant Square Recess

This screw has a similar design to the standard square recess but, like its cousin the tamper-resistant Phillips drive, there is a pin in the center of the recess. This pin requires the use of a specific type of driver. They are typically used in low-torque applications, such as in electronics to help keep consumers from gaining access to the inside components.

Torx®

Often referred to as a “star” drive, this six-pointed socket head was originally developed for the automotive world. However, it can now be found in other products, such as motorcycles, computers, and consumer electronics. At first, these screws were used in areas requiring some level of tamper-resistance, but now they are used in areas that require higher levels of torque due to the design’s resistance to “cam out”. Sizes are listed as T(x) and range from T1 to T100.

Tamper-Resistant Torx®

Also referred to as securityTorx®, these screws are exactly the same as the standard Torx® screw, but have a security post in the center. This post prevents the use of a standard Torx® bit or a slotted screwdriver. You will find more of these screws used in the automotive and electronics industry as the need to protect delicate components from tampering increases.

Torx® Plus

The Torx® Plus design was introduced in the 1990s at just about the same time that the patent for the original design was set to expire. This design features lobes that are more square-shaped. This change reduces the amount of wear on both screw and bit. It also allows for more torque to be used without the risk of damage or “camming out”. It is also designed to be used at high speeds such as those seen on modern factory production lines.

Tamper-Resistant Torx® Plus

This particular form of Torx screw and bit is only available to those who are licensed to use it. You must complete specific paperwork to indicate you are authorized for purchase. This is because the design is intended for use in high-security settings such as correctional facilities. Not only does this configuration have the center post in the screw head, but there are only five lobes instead of the usual six.

External Torx®

This is the exact opposite of the standard Torx® bit in that the torx projects from the head of the screw. Sizes are denominated by the prefix “E” instead of “T”, but do not correspond to the same sizes. The most common use for these screws is in the motor manufacturing industry. They are rarely seen anywhere else.

Interior Hex

Originally called an “Allen” style bit after the first company to produce them, these are extremely common screws, used in a wide variety of applications. The hexagonal shape, with its six flat faces, helps ensure full contact with the driver, but it also tends to create excessive pressure on the corners. This can lead to failure if the interior socket of the head becomes deformed. They are best used in low-torque applications.

Exterior Hex

This is one of the most common screw profiles in use today. The head looks just like a standard nut in that it has six faces that sit at 120 degrees to each other. Not only can you use a hex driver on these screws, you can also use the right size wrench, an adjustable wrench, or either a six or twelve point socket. These screws are good for use in tight spots where a square head would not allow for much turning radius.

Tamper-Resistant Hex

These screws and bits are only available on a very limited basis, as the screws are used by certain manufacturers to protect their equipment from misuse by the end user. They are similar in design to most tamper-resistant screws in that they have a post set in the center of the hole. They are offered in standard fractional sizes as well as metric.

Tri-Wing®

Also referred to as a triangular slotted screw, it has three “slotted” wings, along with a small triangular shaped hole in the center. The slots are offset and do not actually intersect in the middle of the screw head. These screws were developed by Lockheed and the aerospace industry back in the 1970s for use on the L-1011. Today, they are most commonly found in the electronics industry.

Spanner Drive

While the above image shows a pair of holes for the spanner bit to be inserted into, you will find that the more common spanner screws simply have a pair of notches cut into the head. This design is used as a way to prevent tampering and is used in places like public restrooms and elevators. Another common use for these screws is for the soft spikes in golf shoes. There is a three notch version that is used by gun manufacturer Microtech. Leica cameras use something very similar on their rewind knobs and other levers.

One-Way Screws

This is a highly specialized type of screw that can be installed using a standard slotted screwdriver bit. However, the other side of the slots are ramped in the opposite direction. When you try to use a slotted bit to remove them, the bit simply slips out of the screw head. You will find these used to discourage vandals in public restrooms, on VIN plates on vehicles, and in many other locations. They are generally used in applications where removal is unlikely to be necessary.

TA Style Screws

This type of screw has a triangular recess in the head. The sides of the triangle are straight. They are often used in children’s toys, vacuum cleaners, elevators, fan heaters, Master® locks, camping stoves, and Breville® brand kettles. They are used in an attempt to keep consumers from disassembling the products or gaining access to areas where injury can occur.

Spline Drive

The inside of the spline drive screw head has twelve individual splines, as does the driver of the corresponding tool. The splines all have a 60-degree angle, forming three equilateral triangles. They are commonly used in high-torque applications including locking automotive lug nuts and cylinder head bolts. You may also find them in use in other engine bolt applications.

The Final Twist

This is a list of the most common types of screw drive styles in use; there are of course a number of others. Some of these have such limited uses that you are not likely to ever come across them. Others have been out of use for decades. The most important thing to remember is that you should always use the right screwdriver for each type of screw head. Failure to do so could result in screw heads that become too damaged to remove — and in potential injury. The good news is that you can find tools to work with these and just about any other type of screw heads, even those that have been out of production and use for a very long time.

One last thought: be sure to check the condition of your screwdriver bits each time before you use them. A worn or damaged bit can cause severe damage to the screw head, resulting in your having to drill the screws out to remove them. There is always the right tool for any job you are likely to undertake.

Jason Hall
Jason Hall
Hey there, my name is Jason and I am the creator and editor of this site. I have been working in the construction industry for the past 14 years and my mission is to help you start your next renovation!

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