What is the common implement you find in all kinds of machines shops all over the world? You have infinite machines in the world, but all of them have some parts in common. Yes, we are referring to the basic tools like screws, nuts, bolts, and sockets. Thus, you can now say that the gauges, taps, and dies are the most common tools you will find in any machine shop. There is tremendous utility for these tools in every sphere. You need these thread gauges to measure the pitch of the screws and other threaded instruments.
There are two types of threaded instruments in the industry, the internally and the externally threaded ones. The common examples of the externally threaded instruments are the screws, bolts, pipes, etc. Similarly, the internally threaded instruments are nuts, sockets, and again some kinds of pipes and holders. The fitting should be perfect as otherwise it can cause dangerous accidents.
This brings the importance of the thread gauge into the picture. These thread gauges can help in checking out the acceptance of the threaded parts. There are two types of thread gauges, the thread ring gauges and the thread plug gauges. As the name suggests, the ring gauges have use for measuring the pitch of the external threads whereas the plug gauges are instrumental in measuring the pitch of the internal threads.
Both the ring gauges and the plug gauges work on the similar principle of GO and NO GO. The instrument should go through the GO side of the thread gauges with ease without having to force its way. At the same time, it should not go through the NO GO side. The instrument should not move more than two turns on the NO GO side.
There are different types of threads such as NPT thread, UN thread, trapezoidal thread and many more. Accordingly, you have these different types of gauges. They are the solid thread ring gauges and the adjustable thread ring gauges. There is a third type of thread ring gauge known as the thread calliper gauges.
The thread calliper gauge:
Though an external threaded part is best checked with a thread ring gauge, the use of thread caliper gauges (which are also called thread snap gauges) is also in practice. Some caliper gauges may be designed with roller type GO elements, which facilitate quick inspection by simple sliding of the threaded part, using gravity, through the GO rollers.
Though not as accurate as ring gauges in inspection, thread caliper gauges are preferred in mass production areas where screws need to be inspected considerably faster. A caliper gauge is much quicker for inspection as the parts are slid through the gauge rather than screwing-in as in ring gauges. The wear and tear thread caliper gauges is also less.
However, in places where caliper gauges are used, it is normally recommended to also have an additional thread ring gauge set, to perform inspection on random samples and ensure an additional layer of quality assurance.