Parallel Thread for Pipe (G Thread)

Pipe parallel thread is a non-sealing thread. The inner and outer teeth cannot be completely sealed after locking. To prevent leakage, gaskets and O-rings are usually used. You can also wrap anti-leak tape on the surface of the thread, or apply sealant. Its mountain shape has rounded corners, and the angle of the mountain is 55°, marked with G in the ISO 288-1 standard, and is recognized by the German DIN EN ISO 288-1, Japanese JIS B 0202, and British BSP PL and other standard references. PF is the specification name of the old JIS standard. Simply put, G = PF = BSPP.

Thread representation

G [name diameter]

Example

G ⅛

Thread Specifications

Thread Angle: 55° (Rounded profile)
Standard: ISO 288-1, DIN EN ISO 288-1
Type: Non-sealing parallel thread
Application: Pipe connections (G = PF = BSPP)

G Thread Specifications

Unit mm

Name of Thread	Threads per Inch	Pitch P	Major Diameter D, d	Median Diameter D₂, d₂	Minor Diameter D₁, d₁	Drilling Diameter D	Pitch Radius R

Important Note

Non-sealing Thread: G threads are non-sealing parallel threads. After locking, the inner and outer teeth cannot be completely sealed. To prevent leakage, gaskets, O-rings, anti-leak tape, or sealant should be used.

FAQ

What is the difference between G threads and NPT threads?
G threads are parallel (straight) with a 55° angle and rounded profile, while NPT threads are tapered with a 60° angle and sharp profile. G threads require additional sealing methods, while NPT threads can seal through the taper wedging action.
Why are G threads called "non-sealing" threads?
G threads are parallel, so they don't create the wedging action needed for metal-to-metal sealing. The constant diameter means threads can't compress together to form a seal, requiring gaskets, O-rings, or sealant for leak prevention.
What does G = PF = BSPP mean?
These are different names for the same thread standard: G (ISO designation), PF (old Japanese JIS designation), and BSPP (British Standard Pipe Parallel). They all refer to the same 55° parallel pipe thread with rounded profile.
What sealing methods work best with G threads?
Common sealing methods include: flat gaskets or washers on the fitting face, O-rings in grooves, PTFE tape wrapped on threads, liquid thread sealant, or specialized sealing compounds. The choice depends on pressure, temperature, and fluid compatibility.
Can G threads be used with R (tapered) threads?
Yes, G female threads can mate with R male threads because they have the same 55° angle and pitch. This combination is commonly used, with the parallel female thread providing support and the tapered male thread providing the seal.
What are typical applications for G threads?
G threads are used in hydraulic systems, pneumatic connections, instrumentation, and applications where controlled sealing is needed. They're preferred when disassembly is frequent or when precise sealing control is required through external sealing methods.