R Thread vs G Thread: Key Differences and Applications
R threads and G threads are two common types of British Standard Pipe (BSP) threads, widely
used in piping and pneumatic systems. They differ significantly in geometry, sealing method,
and typical application.
Thread Geometry and Standards
R Thread (BSPT – British Standard Pipe Tapered)
Tapered (conical) external thread, in accordance with EN 10226 (ISO 7-1).
Designed to create a pressure-tight seal through the wedging action of the threads
themselves.
Commonly referred to as "R" for male tapered and "Rc" for female tapered threads.
55° thread angle [1] [2] [3] .
G Thread (BSPP – British Standard Pipe Parallel)
Parallel (cylindrical) internal and external threads, in accordance with EN-ISO 228-1.
Does not seal on the threads; instead, sealing is achieved with a gasket or O-ring
outside the thread area (shoulder seal).
55° thread angle [1] [2] [3] .
Sealing Mechanism
Feature
R Thread (BSPT)
G Thread (BSPP)
Thread Type
Tapered (conical)
Parallel (cylindrical)
Sealing Method
Threads themselves seal
Requires external seal
Seal Location
In the thread
At the shoulder (O-ring)
Pressure Applications
High-pressure
Low-pressure
Reusability
Limited (threads deform)
High (threads retain form)
R Thread: The seal is formed by the metal-to-metal contact of the tapered threads, often
enhanced with PTFE tape or sealant. This makes R threads suitable for high-pressure and
vibration-prone applications such as gas and steam lines [1] [3] .
G Thread: The threads themselves do not seal. A gasket or O-ring is compressed between
the fitting faces to achieve a leak-proof connection, making them ideal for low-pressure,
static applications [1] [3] .
Compatibility
Male G (parallel) threads can only be screwed into female G (parallel) threads.
Male R (tapered) threads can be screwed into female G (parallel) or R (tapered) threads [1]
[2] .
Using R threads in polymer components can damage the female thread due to the taper; G
threads are safer for such applications [1] .
Applications
R Threads: Used where a pressure-tight seal is required at the thread, such as in highpressure water, gas, or steam pipelines, and in environments subject to vibration or pressure
surges [3] .
G Threads: Used where the mechanical connection is more important than sealing at the
thread, such as in low-pressure water or air systems, or where an O-ring or gasket provides
the seal [3] .
Summary Table
Aspect
R Thread (BSPT)
G Thread (BSPP)
Standard
EN 10226 (ISO 7-1)
EN-ISO 228-1
Shape
Tapered
Parallel
Seal
In thread (metal/metal)
External (O-ring/gasket)
Pressure
High
Low
Reusability
Lower
Higher
Typical Use
Gas, steam, high-pressure
Water, air, low-pressure
Conclusion
Choose R threads where a built-in, pressure-tight seal is needed, especially for highpressure or dynamic systems.
Choose G threads for low-pressure applications where sealing is provided by an external
component, offering easier installation, repeatability, and better suitability for polymer
connections [1] [3] .
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1. https://www.festo.com/media/cms/media/editorial/downloads/en/White_paper_Threads_IDS.pdf
2. https://www.barthel-armaturen.de/en/threads-types/
3. https://www.kosenvalve.com/media-hub/overview-of-pipe-threads-r-and-g-types.html