R. It is a kind of sealed pipe thread, which has four types: cylindrical internal thread RP, conical external thread R1 matched with cylindrical internal thread; Conical internal thread RC, conical external thread R2 matched with conical internal thread. (when the code specification is written, P, C, 1 and 2 are subscript format).
G. It is an unsealed cylindrical pipe thread
The profile angle of R and G threads is 55 °. There is no distinction between sealed and unsealed pipe threads in China's old drawing standards. The code of cylindrical pipe thread is g and that of conical pipe thread is ZG.
NPT and NPTF are both sealed pipe threads with a tooth profile angle of 60 ° (also known as "American pipe threads", and the above two types are "British pipe threads"), and they are also conical pipe threads. If the code has more than one f, it means "dry seal". American pipe threads also have cylindrical threads. NPT pipe thread was once called taper pipe thread or taper pipe thread in China, code name is Z. Cylindrical thread means that its thread taper is 0, and the taper of conical thread is 1:16.
Difference between pipe thread g and R
» G refers to the pipe thread with non thread sealing: the tooth angle is 55 degrees, and the internal and external threads are cylindrical pipe threads. After matching, they do not have sealing performance, and only play a connecting role in the pipeline. With the help of the sealing ring, they can be used for the low-pressure pipeline under static load. The top and bottom of the teeth are arc-shaped.
» R refers to the pipe thread sealed with thread: the tooth angle is 55 degrees, and it has tightness after tightening. The top and bottom of the teeth are arc-shaped. Taper of taper thread is 1:16. There are two types of fit:
» Cylindrical internal thread / conical external thread, used for low-pressure static load, such as water and gas pipe.
» Conical internal thread / conical external thread, used in high pressure and impact situations.
Purpose of pipe threads G and R
When the thread is used as the sealing surface, the pipe thread shall be sealed; The thread is used for fastening, and the non sealing thread is used when there is another sealing surface: the R thread is sealed with raw material belt, and the G thread is sealed with combined gasket.
Taper pipe thread seal is widely used in Japan, and there is no big problem. The key is the manufacturing accuracy and assembly of pipe fittings. In Japan, sealant is often applied while wrapping the raw material belt. Basically, no leakage can be guaranteed. Europe and the United States tend to use sealing gaskets, but they also have requirements for the accuracy of the joint surface, which is easy to install and maintain. If the two methods are not done well, there will be leakage, which is not absolute.
The taper pipe threaded connection is relatively less airtight than the metric or British g-tooth connection. After a period of time, there will be oil stains (generally anaerobic adhesive can be used) anaerobic adhesive (model: h-330) adhesive is referred to as anaerobic adhesive. It is a one-component sealing adhesive made by using the principle of oxygen to free radical polymerization inhibition, which can be used for both bonding and sealing.  When the coated surface is isolated from the air and catalyzed, it can quickly polymerize and solidify at room temperature. The components of anaerobic adhesive are relatively complex, with unsaturated monomers as the main components, aromatic amines, phenols, aromatic hydrazine, peroxide, etc. in recent years, the formulation of anaerobic adhesive abroad has been constantly innovated and improved, which is favored by the machinery industry.