Thread gauges are a specific type of tool designed to measure the pitch of a screw's threads. Because of this, they are also known as thread pitch gauges.
The threads of an object are put into place when they are carved in a continuing spiral pattern around a cylindrical object like a screw. The variations in how far apart these threads are is known as the pitch, and this small measurement can have a great impact when you are working with something and need to know what other equipment or parts you may need to finish a project.
Using a thread gauge makes it easier for you to find out what type of corresponding bolt to use or what type of hole should be drilled. Once a thread gauge has been used on a threaded object, it's also easier to place the pitch of the screw into a category for later reference if need be. Finally, it can save a lot of valuable time if it keeps you from having to actually measure out the threads and calculate the thread pitch by hand.
Another type of gauge is known as a thread plug gauge. This is an instrument that is used to check the pitch of the ring gauges. This could be done at any point in time, from the original manufacturing process to the recalibration process. When you use this type of thread gauge to measure the threads, you must remember that the two sides of the gauge are going to vary depending on whether or not you are working with a female or male part. The end of the gauge that has a bigger diameter is going to be the one that is designed to measure the female (or internal) threads. If you are measuring the male (or external) threads, then the diameter is going to be slightly smaller.
Mercury thread gauges are manufactured by a company with a wealth of thread gauge knowledge (they manufacture a great variety of gauges). These gauges are made in the United Kingdom and are known for their reliability and their top standards. The lineup of these thread gauges is so extensive and the company has such a wide catalogue that it could take you quite some time to find the Mercury thread gauge that is right for you.