Security Screws – Measuring Up

Security Screws and tamper-resistant fasteners provide additional levels of security to any application or assembly. It is important to choose the correct fastener for the job, otherwise the application will not perform as intended.

Using the exact size fastener is crucial to ensure it fits correctly within the target housing. If the security screw is too big or too small then it will be rendered useless – wasting both valuable time and money.

This raises several questions. How do you measure security screws, and how do you ensure that the measurements you have taken are accurate?

Screw Heads and Screw Length Measurements

The first thing to consider when measuring security screws is the head of the fastener, as this determines how to measure the screw itself.

Security screws with a raised head – ones that don’t sit flush with the target material once installed – are measured from the underside of the head to the tip of the screw. In contrast, screws that host a flat or countersunk head are measured from the top of the head to the tip.

It is important to remember that if the top of the screw protrudes from the target housing once installed, the additional length shouldn’t be considered in your measurement.

Measuring for Machine Security Screws

Security Machine Screws feature a tamper-proof head which typically requires a special tool for installation and removal. The shank of the screw is threaded directly underneath the head to the tip – this is the part that determines the measurement.

The size of a screw is portrayed using two numbers – where the first number  signifies the diameter of the thread and the second number indicates the length of the shank.

The majority of sizes use metric measurements, therefore both numbers provided will be in millimetres. For example, if you are in the market for a security machine screw that has a thread diameter of 10mm and a thread length of 25mm, an M10 x 25mm screw would be right for you.

Although metric measurements are the most common, imperial sizes are also available to order. Please contact us if you are unable to find the correct size, material or finish you require in our product range above, we may be able to supply it.

Security Nut Measurements

Security Nuts are designed to be used alongside a security machine screw, therefore the measurements of the nut will depend on the corresponding security screw.

In order to determine the correct size security nut, you will need to know the diameter of the screw thread. The thread diameter of the nut, or the ‘M’ number, should match the ‘M’ number of the security screw.

Another important consideration is to ensure that the thread pitch of the nut matches that of the screw. This is the distance between each thread. For example, an M8 x 1.25mm thread (known as standard pitch or coarse thread) will not be compatible with an M8 x 1mm thread (known as fine pitch).

If you are working with a security barrel nut, it is important to know the length of barrel and the length of the internal thread, as well as the thread diameter. To ensure the barrel nut fits correctly with the screw once installed, the thickness of the installation material should also be taken into account.

Self-tapping Security Screw Gauges

Whilst millimetres are the most common unit of measurement for most types of screw, this does not apply to self-tapping security screws. The length of self-tapping screws are provided in inches, while the thread diameter is given using the gauge measurement.

This is difficult to measure accurately without using the correct tools, so we have converted the gauge measurements for our self-tapping fasteners into millimetres to make the measuring up process as easy as possible. An example of this can be found in our 6 Lobe Pin TX Button Self Tapping Security Screw.

Need more help choosing Security Screws?

Fastenright supply an extensive range of security screws which can be found above. Here you will find all of the standard sizes, materials and finishes that we offer. If you are still unsure about how to find the right screw for you, or if the security screws you require are not listed, please contact us. Our team will be happy to offer advice and guidance.