The Purpose of a Standard Thread Gauge

Thread gauge is a generic term for measuring thread in various contexts, from machinery to textiles, and comes in multiple forms.

In an industrial context, getting thread gauge wrong can cause a minor issue and only require a quick fix. In some industries, such as medical and aeronautics, it can cause something more catastrophic. So having an understanding is vital when working with threads.

This guide explains the purpose of a standard thread gauge and how you can apply it to your industry to help along the way.

What is Standard Thread Gauge?

A standard thread gauge is a device used to measure the pitch, form, and threads' depth. The indicator is also often applied to bolt holes to analyse the size of the hole. It will typically be an inexpensive tool used in the industry that will allow you to distinguish between different threads.

These tools come in aluminium, steel, or cast-iron forms. The most basic style has a measuring scale marked out on it, including BSPT (British Standard Pipe Thread) and BA (British Association). Also, standard thread gauges have two measuring plates, which makes them particularly useful for industrial applications.

However, the strength of the gauge weakens when made for a cheap cost. For example, a ring gauge (a type of thread gauge) may be made from aluminium and only allow you to measure bolt holes that are 10mm in diameter. In industrial applications, you might need to use a ring gauge that measures spots that are 25mm wide.

How Do You Know Which to Buy?

It can be not very clear to see such a vast array of price points, anywhere from £1 to £1000 and above. But like many industrial tools, they serve different purposes; when you realise this, spending £1 might be better for your needs than £1000, and vice-versa.

For example, thread gauges at the bottom-end of the market are often produced from cast iron or steel and then machined down by hand until it forms the correct size. However, these gauges are still used for measurement purposes due to their low cost and therefore are useful in many industries for daily use. They are instrumental if you need to keep track of thread sizes on-the-go because they are relatively easy to carry around.

The problem with this process is that human error can creep in. For example, a machinist may have minor issues with his tools or might not entirely focus their mind on the task at hand.

As a result, the gauge doesn't come out as perfect as it should be. Therefore, in specific industries where high-levels of precision are required, consulting professionals can save your business much money in repairs in the future.

What Are the Other Types of Thread Gauges?

Of course, standard thread gauges are the most popular type, but even if you aren't using any others, it helps to know the differences. Other thread gauge types include:

Ring Gauge

This is a gripping tool of some sort used to measure bolt holes' size. It comprises metal or plastic and is available in various sizes. It is one of the most popular types of thread gauge for measuring bolt holes sizes. However, it doesn't often allow you to measure thread pitch accurately.

Flexible Ring Gauge

This is an alternative to the ring gauge. Still, to measure diameters, it uses an adjustable grip rather than a ring. It can be marginally more expensive than traditional ring gauges and, therefore, less popular.

Contour Gauge

This is a device you can use for both thread pitch and form measurement purposes. It doesn't use any fitting as such, so it will never break when using it. It also has the same size permanently fitted to it to not change during measurement purposes.

Micrometre Gauge

This is a device that's used to measure diameters. It's very accurate and easy to use. Still, if you need something to measure thread form, you need to look elsewhere.

Semi-Joint Gauge

This tool accounts for thread pitch measurement and comes in two separate parts. These parts will then lock together at a certain point. The two are usually connected by a spring, allowing the gauge to move freely from one position to the next.

Thread Plug Gauge

This is a device that can screw into existing threads. The gauge has a hole in the middle that allows you to see the thread pitch size underneath it. It's generally used as a temporary gauge until you have the chance to use one of the other meters mentioned above.

How To Use a Standard Thread Gauge

Standard thread gauges can be used in two ways, depending on the end goal, as a measuring tool and an inspection tool. Whichever you use, it's essential to choose the correct gauge size following the hole you want to measure. Using the incorrect calibration or an old gauge that is dirty and neglected can lead to significant errors.

Measuring Thread Size

To use a thread gauge as a measuring tool, you first need to identify what you are trying to measure. For this, you need to know the nominal size of the part. You can write this on the drawing or instructions for the piece in millimetres.

You then need to take the thread gauge and screw it into the part. You do this by matching your thread size with the corresponding size on the thread gauge.

For example, if you measure a 1/4 inch pitch, and the thread gauge has a pitch of 0.25 on it, you know that the correct size is a 1/4 inch. Once you have aligned the thread gauge in place, then it needs removing from the part.

You will see how well-aligned your measurement is by looking at the distance of thread between each larger hole on the threaded area of your part. If there is more space between each hole than what you were expecting, your work requires adjustments to meet industry standards. Finally, use callipers and measure if your threaded hole is indeed as large as it should be.

Using a standard threaded bolt, you can use a standard nut of a similar diameter to secure the thread gauge. The nut will allow you to take measurements that are accurate enough for your needs.

Inspection Thread Size

If you don't know what measurement you are looking for, you can use a thread gauge as an inspection tool instead. If you need to determine if the parts fit for purpose or do not meet safety standards, using a thread gauge is an excellent tool in your arsenal.

If you are looking to inspect a threaded joint, you need to ensure that the thread gauge is in the same position as the original thread. This position will allow you to see any deviations between your part and the new one.

The same goes for if you are inspecting a line. If the original thread's thicker or thinner than the one you have to replace, you would need to adjust your thread gauge position so that it matches.

You can also use a thread gauge for inspection purposes in non-threaded parts where a smaller surface area needs inspection. To do this, you screw the thread gauge into the small hole and examine it from different angles. You can then apply an adequate inspection.

QC Your Standard Thread Gauge

Even though standard thread gauges won't give the most precise measurements, they can still determine if a bolt or screw has thread damage or not. You can also use the standard thread gauge to check the thread pitch.

If you want to know your bolt or screw's length, then this is where you need to look. As long it's clean and doesn't over-tighten any threads, your measurements should be correct and up to par with other options that you have available.

Also look out for certification services, which give reassurance that what you're buying is of the highest accuracy.

Standard Thread Gauges for All Tasks

Suppose you want to know the size of threaded holes and don't have access to the best technology globally. In that case, a standard thread gauge will undoubtedly be useful.

They are easy to carry around, affordable, and provide you with what you need! If you are stuck in the middle of nowhere and need to check the thread size of a screw, this is where you go. They are not as accurate as other options, and you have to be very careful with them, but they will get the job done.

If you need some thread gauges, visit our store today. Get to know these different thread gauges in more detail to find the right one for your needs.

If you have any questions about any of our engineering tools, please call us on 01527 520 580

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