The new Unified Coarse Thread is comparable with the ISO metric thread that has been in use for ages. It defines a standard thread form and series along with allowances, tolerances and designations for screw threads that are commonly used in many countries including the United States. The UNC Thread Gages differs from the ISO metric screw thread that was been formally used for bolts and nuts in terms of the screw thread outer diameter and the pitch which is used as an inch fraction rather than the millimeters value in ISO metric screw Gages. However, both have the same 60 degrees profile. A unified thread standard UNC Thread Gages can be mechanically interchangeable with a USS thread is of the same diameter. These threads are designed according to certain rules and they are used according to America developed system. When it comes to measuring or verifying the size of any screw thread, it is advisable to consider the thread Gauges before taking any action because any attempt to measure Metric Thread with an imperial gauge will not return accurate result. 

Your Metric Thread Gauges needs to be periodically calibrated in the standard room to check if they are still in a standard usable thread in order to prevent the wear and tear that often arise in screw thread due to their constant usages. There are a number of moving parts on engineering equipment that keeping and maintaining them is a necessity so as to enable them to function properly. Series of Metric Thread Gauges are manufactured per ASME B1.16M that can be purchased individually or as burden. They are used to ensure the proper assembly of creating parts of mating parts, for inspecting the functional thread and pitch diameter. A 1 /4 nominal screw diameter could have a UNC 1/4 to 20threads and this implies that the screw thread has a 20threads per inch. The selection of unified coarse screw thread for any engineering activities will depend on the specific applications on the machine. 

UNC Thread Gages is one of the most common screw thread types of being used and they come in in three different classes. These are as follows:

Class 1: This thread Gages are typically used for applications that require a liberal tolerance so as to permit the easy assembly of the moving parts. The class 1 screw thread that can be either internal or external. 

Class 2: They are found in many ways compartments and equipment because they are the best most common name class for general applications. 

Class 3: In applications where the closeness of fit in and accuracy of threads elements are of importance, the class A UNC Thread Gages is considered the best option to be used. 

The Metric Thread Gages also uses the same thread geometry as the USS standard except that the former differs from the later in terms of the Metric units of the screw thread pitch and the screw thread diameter.