You should to know the basic knowledge of the thread gauges

What is thread gauges? – Parts4world.com

The thread gauges is a gauge used to check whether the thread meets the mechanical connection requirements.

Thread plug gauges are used to inspect internal threads, and thread ring gauges are used to inspect external threads.

Thread is an important and commonly used structural element. Threads are mainly used for structural connection, sealing connection, transmission, reading and load-bearing occasions. From general use conditions to harsh conditions (high temperature, high pressure, severe corrosion), from rough to very precise, in short, it is widely used.

Classification of the threads:

1. Ordinary thread (also known as American thread or metric thread) M

2. American standard uniform thread is UNC, UNF, UNEF, UN, UNS series

3. Non-thread-sealed pipe thread (old nominal cylindrical pipe thread)

4. Trapezoidal thread

5. Other threads

NPSM – National Pipe Straight Mechanical thread.  American Standard Straight Pipe Thread for Mechanical Connection: These internal and external threads are used for free mechanical parts connection without internal pressure. The product has a straight pipe GO and NO GO ring or plug gauge inspection.

NPSL – National Pipe Straight Locknut (or Loose) thread.  Straight pipe threads for American standard lock nuts: These internal and external threads are used for mechanical matching of anti-feeding threads.

NH – National Hose thread.  American Standard Fire Hydrant Thread: These internal and external threads are used for fire hydrants, garden hoses, chemicals and elevators.

NPSH – National Pipe Straight Hose thread.  American standard hose connection thread: These internal and external threads are used for steam, air, water and other standard pipe connections.

NPSC – National Pipe Straight Coupling thread.  American standard pipe connection with straight pipe thread: The pipe joint has the same profile as the inner straight pipe thread. When the outer taper thread NPT is used for the assembly of the sealing packing, it can be tightened by a wrench. Usually it can form a sealed connection. It is mostly used for low pressure pipes. Road system.

NPSF – National Straight Pipe for Fuels thread.  American standard oil circuit dry sealing thread: these internal threads are used for soft materials or ductile iron parts without sealing and NPTF external thread assembly.

NPSI – National pipe straight-intermediate thread.  American Standard Dry Seal Intermediate Thread: These internal threads are used for the assembly of hard or brittle materials with short PTF-SAE external threads, but they can also be used for full-length assembly of NPTF external threads.