Quick answer
To order pipe thread gauges, send the full thread designation (for example 1/2-14 NPT or R 1/2 / G 1/2), whether the thread is internal or external, the gauge type (L1 plug, L1 ring, L2/L3, or GO/NO-GO for straight threads), the standard, quantity, calibration certificate needs and delivery country. GageTools supplies pipe thread gauges with an MOQ of 1 piece and replies to RFQs within 24 hours.
Pipe thread gauges are one of the most common sources of ordering mistakes. NPT and BSPT look similar but are not interchangeable, taper gauges are read differently from straight-thread gauges, and one missing letter (G vs R, NPT vs NPTF) changes the gauge completely. This checklist helps you get the right gauge on the first order.
Step 1: Confirm the Thread Family
| Thread | Type | Standard | Typical designation |
|---|---|---|---|
| NPT | Taper, sealing with sealant | ASME B1.20.1 | 1/2-14 NPT |
| NPTF | Taper, dryseal | ASME B1.20.3 | 1/2-14 NPTF |
| NPSM / NPSC | Straight pipe threads | ASME B1.20.1 | 1/2-14 NPSM |
| BSPT (R / Rc / Rp) | Taper or parallel sealing | ISO 7-1 / EN 10226 | R 1/2, Rc 1/2, Rp 1/2 |
| BSPP (G) | Parallel, non-sealing | ISO 228-1 | G 1/2 A, G 1/2 B |
If you are not sure which thread you have, see NPT vs NPTF vs BSPP vs BSPT before ordering. Never use an NPT gauge on a BSPT thread or the other way round – the angle (60° vs 55°) and pitch differ.
Step 2: Internal or External Thread?
- Internal thread (fitting body, port): you need a plug gauge.
- External thread (pipe end, nipple): you need a ring gauge.
- Many buyers order both, plus setting plugs for ring gauges where required.
Step 3: Choose the Gauge Type
For taper threads (NPT, NPTF, BSPT):
- L1 plug and L1 ring gauges check hand-tight engagement – the standard gauges for most NPT work. See NPT L1 plug and ring gauges.
- L2 / L3 and 6-step gauges are used for NPTF dryseal threads and more detailed inspection.
- Taper gauges are read against a step or notch tolerance – the gauge face must fall within the allowed step, not just “go on”.
For straight threads (BSPP / G, NPSM):
- Use GO/NO-GO plug and ring gauges, just like metric threads. For G threads, state class A or B for external threads.
Step 4: Add Quantity, Documents and Delivery
- Quantity per size – MOQ is 1 piece.
- Calibration certificate: a calibration certificate is available on request; third-party CNAS calibration usually adds about 3 working days. See certificate requirements if your customer specifies them.
- Delivery country and required date. Standard stock sizes ship within 72 hours; custom or non-stock gauges typically take 10–15 working days.
Ordering Checklist
| Item | Example |
|---|---|
| Thread designation | 3/4-14 NPT, Rc 1/2, G 1 B |
| Internal or external | Internal (port) |
| Gauge type | L1 plug gauge |
| Standard | ASME B1.20.1 / ISO 7-1 / ISO 228-1 |
| Quantity | 2 pieces |
| Certificate | Calibration certificate, or CNAS third-party |
| Delivery | Country, postcode, required date |
Send Your Pipe Thread Sizes for a Quote
Send these details and we reply with a written quotation within 24 hours:
- Full thread designation, e.g. 1/2-14 NPT or G 1/2 B
- Internal or external thread, plug or ring gauge
- Gauge type (L1, L2/L3, GO/NO-GO) and quantity
- Certificate needs, delivery country and required date
Common Ordering Mistakes
- Writing “1/2 inch pipe thread” only. This could be NPT, BSPT or BSPP – always give the full designation.
- Ordering NPT gauges for BSPT parts (or vice versa) because they look similar.
- Forgetting the setting plug when your quality system requires ring gauges to be checked.
- Ignoring the step tolerance on taper gauges and treating them like GO/NO-GO gauges. See taper pipe thread inspection mistakes.
- Leaving out the certificate and requesting it after shipment, which can delay delivery.
Browse all thread gauges or send your list on the quote form.
FAQ
What information do I need to order an NPT gauge?
The full designation (for example 1/2-14 NPT), internal or external thread, gauge type such as L1 plug or L1 ring, quantity, certificate needs and delivery country.
Can I use an NPT gauge to check a BSPT thread?
No. NPT uses a 60° thread angle and BSPT uses 55°, and many pitches differ. Always use the gauge for the exact thread standard.
Do BSPP (G) threads need taper gauges?
No. BSPP is a parallel thread, so it is checked with GO/NO-GO plug and ring gauges. For external G threads, state class A or B.
How fast can you ship pipe thread gauges?
Standard stock sizes ship within 72 hours. Non-stock or custom gauges typically take 10–15 working days, confirmed on the quotation.