Thread plug and ring gauges
JBO Thread Gauges Plug and Ring Gauges for Every Thread.
4,774 JBO thread gauges, delivered across the UK: Go/NoGo, GO and NoGo thread plug gauges and GO and NoGo thread ring gauges for metric coarse and fine, Unified, BSP, BSPT, NPT, NPTF, BSW, BSF, trapezoidal, Pg and conduit threads, plus STI plug gauges for wire thread inserts.
The JBO range
Shop JBO Thread Gauges by Thread
Plug gauges check internal threads in tapped holes. Ring gauges check external threads on bolts and studs. Start with the thread standard.
149Metric Coarse Plug Gauges
Thread plug gauges for checking internal metric coarse threads, double-ended or as single GO and NoGo gauges.
Shop metric coarse plugs
331Metric Coarse Ring Gauges
Thread ring gauges for checking external metric coarse threads on bolts, studs and screws.
Shop metric coarse rings
1,103Metric Fine Plug Gauges
Go/NoGo, GO and NoGo thread plug gauges for internal metric fine threads.
Shop metric fine plugs
1,995Metric Fine Ring Gauges
GO and NoGo thread ring gauges for external metric fine threads.
Shop metric fine rings
242Unified Plug Gauges
Thread plug gauges for internal Unified threads, double-ended Go/NoGo or single GO and NoGo.
Shop Unified plugs
459Unified Ring Gauges
GO and NoGo thread ring gauges for external Unified threads.
Shop Unified rings
182BSP & BSPT Gauges
Plug and ring gauges for BSP (G) parallel pipe threads and ring gauges for BSPT (R) taper threads.
Shop BSP gauges
52NPT & NPTF Gauges
Plug and ring gauges for NPT and dryseal NPTF taper pipe threads.
Shop NPT gauges
97BSW & BSF Gauges
Plug and ring gauges for BSW and BSF threads, for older British machinery and repairs.
Shop BSW and BSF gauges
110Trapezoidal, Pg & Conduit
Plug and ring gauges for trapezoidal lead screw threads, Pg cable gland threads and electrical conduit threads.
Shop these gauges
54STI Plug Gauges
Plug gauges for holes tapped to take helical wire thread inserts (Helicoil type), metric and UNC.
Shop STI gaugesComparing thread gauges from every brand? See all thread gauges, or read our guides to choosing the right thread gauge and using thread gauges.
Find your gauge
JBO Thread Gauges by Type
Pick the thread standard, then the gauge type. Each number is how many sizes we list; click it to shop them.
| Thread | Plug Go/NoGo | Plug GO | Plug NoGo | Ring GO | Ring NoGo | Ring Go/NoGo |
|---|---|---|---|---|---|---|
| Metric coarse | 125 | 12 | 12 | 165 | 166 | – |
| Metric fine | 539 | 283 | 281 | 998 | 997 | – |
| Unified | 218 | 12 | 12 | 228 | 231 | – |
| BSP (G) | 19 | 22 | 22 | 48 | 47 | – |
| BSPT (R) | – | – | – | – | – | 24 |
| NPTF | 12 | – | – | – | – | 12 |
| NPT | 14 | – | – | – | – | 14 |
| BSW | 16 | 2 | 2 | 18 | 17 | – |
| BSF | 14 | – | – | 14 | 14 | – |
| Trapezoidal | 14 | – | – | 14 | 14 | – |
| Pg | 7 | 3 | 3 | 10 | 9 | – |
| Electrical conduit | 8 | 3 | 3 | 11 | 11 | – |
| STI metric | 26 | – | – | – | – | – |
| STI UNC / UNF | 28 | – | – | – | – | – |
Calibration
Add a Calibration Certificate
Need a certificate for your quality system? Add one to each gauge when you order.
- UKAS certificate: screw plug gaugesFor thread plug gauges up to 100mm. One certificate per gauge, up to 14 days from stock.
- UKAS certificate: screw ring gaugesFor thread ring gauges up to 100mm. One certificate per gauge, up to 14 days from stock.
- Custom certificateFor anything else, call the office for price and delivery.
Choosing a gauge
Choose a JBO Thread Gauge in Four Steps
Answer these and the finder table will point you to the right gauge.
- 1
Thread
Read the thread off the drawing: for example M8 x 1.25 is metric coarse, M8 x 1 is metric fine, 1/4-20 UNC is Unified.
- 2
Plug or Ring
A plug gauge checks an internal thread in a tapped hole. A ring gauge checks an external thread on a bolt or stud.
- 3
GO, NoGo or Both
A double-ended Go/NoGo plug does both checks in one tool. Ring gauges come as separate GO and NoGo rings.
- 4
Tolerance
Match the tolerance class on the drawing, for example 6H for internal and 6g for external metric threads.
Questions
JBO Thread Gauges: Common Questions
Plug gauge or ring gauge?
A thread plug gauge checks an internal thread, such as a tapped hole. A thread ring gauge checks an external thread, such as a bolt or stud. Choose the gauge for the thread you are inspecting, not the part that mates with it.
What do GO and NoGo mean?
The GO side should screw fully into or onto a good thread. The NoGo side checks the thread is not oversize (internal) or undersize (external): it may start, but should not screw in by more than about two turns. If the GO enters and the NoGo does not, the thread is within tolerance.
What do 6H and 6g mean?
They are ISO metric tolerance classes. A capital letter, as in 6H, is for internal threads and a lower case letter, as in 6g, is for external threads. 6H and 6g are the standard medium fit for most metric threads. Match the class shown on the drawing.
What is an STI gauge?
STI stands for screw thread insert. A hole that will take a helical wire thread insert (Helicoil type) is tapped larger than the nominal thread, so it needs its own STI plug gauge to check it before the insert is fitted.
Can I get a calibration certificate?
Yes. Add a UKAS calibration certificate for each screw plug or screw ring gauge when you order, up to 14 days from stock. For anything else, call the office for a custom certificate.
Can I buy JBO thread gauges in the UK?
Yes. Protool supplies the JBO range on this page across the UK, with free next day delivery on orders over £50 ex VAT and same day dispatch on orders placed by 4.30pm.
Not Sure Which Gauge You Need?
Send us the thread callout from the drawing, or a JBO part number, and we will find the right gauge. Everything here ships from Kent.
