Pipe Thread Gauges
BSP Thread Gauges: G, R and Rc Pipe Thread Plug and Ring Gauges
GO/NO-GO plug and ring gauges for British Standard Pipe threads: parallel G (BSPP) threads to ISO 228 and pressure-tight R, Rc and Rp (BSPT) threads to ISO 7. Standard sizes from 1/16 to 4 inch, plus custom pipe thread gauges made to your drawing.
Product Types
BSP Plug and Ring Gauges We Supply
Use plug gauges for internal pipe threads and ring gauges for external pipe threads. Each gauge is marked with the thread size and GO / NO-GO.
G Thread Plug Gauges (BSPP)
GO/NO-GO plug gauges for parallel internal G threads to ISO 228. Used on hydraulic fittings, valves and pump housings.
G Thread Ring Gauges (BSPP)
GO/NO-GO ring gauges for parallel external G threads, class A or class B. Ask us about matching setting plugs for ring gauges.
Rc Taper Plug Gauges (BSPT)
Taper thread plug gauges to ISO 7-2 for internal Rc threads. The gauge step shows whether the gauging plane is within tolerance.
R Taper Ring Gauges (BSPT)
Taper thread ring gauges for external R, R1 and R2 threads used in pressure-tight pipe joints.
Rp Parallel Plug Gauges
Plug gauges for Rp parallel internal threads that seal with R1 taper external threads.
Custom Pipe Thread Gauges
Special sizes, extended handles or gauges made to your drawing. Send the drawing and we will check feasibility.
Size Chart
Common BSP Thread Gauge Sizes
Basic dimensions per ISO 228-1 and ISO 7-1. G and R threads share the same pitch and major diameter for each size.
| Size (inch) | G / R / Rc designation | Threads per inch | Pitch (mm) | Major diameter (mm) |
|---|---|---|---|---|
| 1/16 | G1/16 / R1/16 / Rc1/16 | 28 | 0.907 | 7.723 |
| 1/8 | G1/8 / R1/8 / Rc1/8 | 28 | 0.907 | 9.728 |
| 1/4 | G1/4 / R1/4 / Rc1/4 | 19 | 1.337 | 13.157 |
| 3/8 | G3/8 / R3/8 / Rc3/8 | 19 | 1.337 | 16.662 |
| 1/2 | G1/2 / R1/2 / Rc1/2 | 14 | 1.814 | 20.955 |
| 3/4 | G3/4 / R3/4 / Rc3/4 | 14 | 1.814 | 26.441 |
| 1 | G1 / R1 / Rc1 | 11 | 2.309 | 33.249 |
| 1-1/4 | G1-1/4 / R1-1/4 / Rc1-1/4 | 11 | 2.309 | 41.910 |
| 1-1/2 | G1-1/2 / R1-1/2 / Rc1-1/2 | 11 | 2.309 | 47.803 |
| 2 | G2 / R2 / Rc2 | 11 | 2.309 | 59.614 |
| 2-1/2 | G2-1/2 / R2-1/2 / Rc2-1/2 | 11 | 2.309 | 75.184 |
| 3 | G3 / R3 / Rc3 | 11 | 2.309 | 87.884 |
| 4 | G4 / R4 / Rc4 | 11 | 2.309 | 113.030 |
Need a size that is not listed? Send the thread designation and we will quote it.
Selection
How to Choose the Right BSP Gauge
- Parallel or taper? G and Rp threads are parallel; R and Rc threads are tapered. Taper threads need taper gauges.
- Internal or external? Plug gauges check internal threads; ring gauges check external threads.
- Tolerance class: external G threads are class A or class B, so state the class on your enquiry.
- Not NPT: BSP threads have a 55° angle and NPT threads 60°, so NPT gauges cannot be used on BSP parts.
For a full explanation of BSPP vs BSPT and how to identify pipe threads, read our BSP thread gauge guide and how GO/NO-GO thread gauges work.
FAQ
BSP Thread Gauge FAQ
What is the difference between G and R thread gauges?
G threads (BSPP, ISO 228) are parallel and are checked with GO/NO-GO plug and ring gauges. R, Rc and Rp threads (BSPT, ISO 7) are pressure-tight pipe threads; taper R and Rc threads are checked with taper plug and ring gauges that show where the gauging plane sits within its tolerance.
Can I use an NPT gauge to check a BSP thread?
No. BSP threads use a 55 degree thread angle while NPT uses 60 degrees, and the threads per inch differ for most sizes. An NPT gauge will give false results on a BSP thread, so always use a gauge made for the BSP standard on your drawing.
Which gauge do I need for an Rc internal thread?
An Rc (taper internal) thread is checked with an Rc taper thread plug gauge to ISO 7-2. For an Rp parallel internal thread used with R1 external threads, use an Rp plug gauge. Tell us the exact designation on your drawing and we will confirm the right gauge.
What information should I send for a BSP gauge quote?
Send the thread designation (for example G1/2-A, R1/2 or Rc3/4), whether you need plug gauges, ring gauges or both, the quantity, and your drawing or standard if you have special requirements.
Get a Quote for BSP Thread Gauges
Send the thread designation, gauge type and quantity. We reply with a quotation for your sizes.