Pipe thread taps are used to tap internal pipe threads on pipes, pipeline accessories and general machine parts, including G series and Rp series cylindrical pipe thread taps and Re, NPT series tapered pipe thread taps, etc. G is the code of the 55° unsealed cylindrical pipe thread, with cylindrical inner and outer threads (only for mechanical connection, not for sealing); 

Rp is the inch sealed cylindrical inner thread (for mechanical connection and Sealing function); Re is the code of the inch sealing conical internal thread; 

NPT is the conical sealing pipe thread with a 60°tooth angle. Metric thread is a 60-degree equilateral thread, which is expressed by pitch. Inch thread is an isosceles 55-degree thread, and American and British threads are expressed by the number of threads per inch.