We have seen various types of thread ring gauges and thread plug gauges. We have also seen the importance of the thread calliper gauges. These gauges have tremendous utility in the manufacturing industry. No industry is ever complete without these gauges. In this article, we shall discuss about the thread pitch gauge and understand its concept.
The thread pitch gauge
A thread pitch gauge is a visual checking device to identify the pitch of a threaded part and it is NOT a typical metrology/inspection device. When you come across a new screw or a nut and you are not sure whether it is a metric thread, British thread, or any other thread and you need to quickly check the pitch and, to an extent, the profile, you can make use of a thread pitch gauge.
A pitch gauge usually comes as a set of thin plates or leafs, with hacksaw-like teeth precisely machined to a given thread pitch (or TPI – threads per inch) and thread profile (specific flank angle and tooth depth). You have to pick out one plate (leaf) from the gauge, try to match it with the threaded part, and if it does not fit snugly, try another plate in the gauge.
When all the teeth in a specific gauge leaf sit properly on the part being measured (i.e. without a gap), you can read the pitch size engraved in the leaf of the gauge in use. By looking at the light-passing between the gauge and the part, you can, to some extent, decide about the matching of the flank angle of the thread as well.
But a pitch gauge is not a one hundred percent foolproof device to check and determine a thread pitch and type. Unless the inspector is experienced, there is the possibility of making a mistake in determining the correct pitch/ thread type, particularly if the thread is too fine and the pitch happens to be close to a nearby metric /SAE size thread.
Again: a pitch gauge is only a visual comparator. It does not decide acceptance or non-acceptance of a threaded part like a GO/NO-GO gauge. It is not a metrology device in the strictest sense.
Understanding these various types of gauges is important because you need these implements in the industry to check out the tolerance levels of the screws and other industrial equipment. These screws are used in various important machineries like aircrafts and ships. Just imagine what will happen if a simple screw just flies out of the aircraft while it is cruising at a high altitude. The screw can lodge itself in the engine parts and create havoc thereby putting the lives of hundreds of people in danger.
This is why you have strong threaded screws like the ACME threads and the trapezoidal threads on the aircraft doors. They function as lead screws in a way. Thus, you find the trapezoidal thread gauge of great importance in the aviation and maritime industry. Many a life depends on the simple tolerance test of these screws and other instruments.