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Thread plug gauge M12x1.25 6H
15366
€32.37 tax inc.
Net price: €26.32
Description
THREADM12x1.25
TOLERANCE6H
STANDARDISO 1502
MATERIALTool steel
M12x1.25 6H GO/NO-GO thread plug gauge
Internal thread gauge according to PN-ISO 1502:1998
| TECHNICAL DATA | |
|---|---|
| Thread type | ISO metric fine thread (MF) |
| Thread size | M12x1.25 |
| Thread pitch | 1.25 mm (fine) |
| Tolerance class | 6H |
| Pitch diameter (D2) | 11.188 mm |
| D2 range for 6H | 11.188 – 11.368 mm |
| Minor diameter (D1) | 10.647 mm |
| Gauge type | GO / NO-GO |
| Material | Tool steel, hardened |
| Hardness | 58–62 HRC |
| Standard | PN-ISO 1502:1998 |
1
GO end — longer thread with a full profile. It is screwed in by hand through the full length of the hole.
2
Handle engraved M12x1.25-6H — size and tolerance class of the inspected hole.
3
Red ring — identifies the NO-GO end.
4
NO-GO end — shorter thread with a truncated profile. It checks only the pitch diameter, so it is allowed to enter by 2 turns.
Thread plug gauge M12x1.25 6H shows within seconds whether a tapped hole is within tolerance 6H. The GO end GO must enter by hand through the full thread length. The NO-GO end NO-GO must not enter by more than 2 threads, counted when unscrewing the gauge. If both conditions are met, the thread is acceptable.
The M12 × 1.25 fine thread is found in machine parts, hydraulic systems, and automotive fittings — wherever a joint must hold its setting and resist loosening from vibration. Check the pitch: the M12 diameter is available in four versions — coarse pitch 1.75 mm and fine pitches 1.5, 1.25, and 1 mm. The gauge applies only to the version 1.25 mm; the others have a different pitch diameter. For reference: the thread minor diameter M12x1.25 is 10.647 mm, while the gauge checks the pitch diameter, which is the dimension halfway up the thread profile.
Operating principle: GO / NO-GO
How to check an internal thread correctly
1
The GO end is screwed in by hand, without force, along the full length of the M12x1.25 thread.
2
The NO-GO end stops after no more than 2 turns — turns are counted when unscrewing.
3
The GO end passed, the NO-GO end stopped — the hole is within class 6H.
Thread inspection in 3 steps
1 GO end (longer thread)
Screwing into the thread — must enter
2 NO-GO end (red)
Screwing into the thread — no more than 2 turns
✓ Acceptable thread
Tolerance: 6H OK
If the end GO enters, and the end NO-GO does not enter — the thread meets the requirements of class 6H according to PN-ISO 1502:1998
GO end (passes)
No color marking — it has a longer thread and GO marked on the handle. It checks minimum thread dimensions (D2 min = 11.188 mm) and must screw in over the full length. If it does not enter — the thread is undersized.
NO-GO end
Marked with a red ring. Checks maximum thread dimensions (D2 max = 11.368 mm) and must not engage more than 2 threads, counted when unscrewing.
✓ Thread acceptable — GO enters the full length, NO-GO stops.
✗ Thread too tight — GO does not enter the hole.
✗ Thread too loose — NO-GO enters more than 2 turns.
Tolerance class 6H for an M12x1.25 thread
Comparison of tolerance classes for an M12x1.25 internal thread
Comparison of classes 4H, 5H and 6H
Basic pitch diameter D2 for the thread M12x1.25 is 11.188 mm. In classes designated H, this is also the minimum dimension — the tolerance extends upward only.
| Class | D2 nominal [mm] | D2 permissible [mm] | Tolerance zone | Application | Status |
|---|---|---|---|---|---|
| 4H | 11.188 mm | 11.188 – 11.300 mm | 0.112 mm | Precision | |
| 5H | 11.188 mm | 11.188 – 11.328 mm | 0.140 mm | Close | |
| 6H | 11.188 mm | 11.188 – 11.368 mm | 0.180 mm | Standard | THIS PRODUCT |
The full range of class 6H is 0.180 mm. Class 6H corresponds to a typical nut and a standard machine tap — it is selected for 6g bolts; 4H and 5H reduce clearance, while 7H leaves an allowance for coating. The table gives pitch diameter D2, not the tap drill diameter.
Correct use and storage
Usage rules according to ISO 1502
Before measurement, remove chips and oil from the hole. Screw in the gauge by hand only, without a tap wrench or other wrench. Reference temperature: 20 °C. Store the gauge in its case, protected with rust-preventive oil. The user determines the calibration interval — ISO 1502 (clause 7.2.1) requires periodic measurement but does not specify an interval.
INCLUDED:
| ✓ | M12x1.25 6H GO/NO-GO thread plug gauge |
| ✓ | Size and class marking on the plug |
| ✓ | Tool steel hardened to 58–62 HRC |
Frequently asked questions
6H is the most commonly used internal thread class: the digit 6 specifies the width of the tolerance zone (0.180 mm for M12x1.25), and the letter H specifies its position relative to the nominal size (lower deviation equal to zero). A 6H thread mates with a 6g bolt and corresponds to a typical nut and a standard machine tap.
No. The pitch diameter is, for M12 × 1.25 11.188 mm, for M12 × 1 — 11.350 mm, and for M12 × 1.5 — 11.026 mm. The differences reach tenths of a millimeter, and from the first few threads the gauge will either fail to enter or screw in without resistance.
The thread is nonconforming, when the GO end does not screw in over the full length (D2 below 11.188 mm — thread too tight) or the NO-GO end engages more than 2 turns (D2 above 11.368 mm — thread too loose). Standards: ISO 965-1 (tolerances), ISO 1502 (inspection procedure).
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