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Thread plug gauge M18x1.5 6H
14368
€51.79 tax inc.
Net price: €42.11
Description
THREADM18x1.5
TOLERANCE6H
STANDARDISO 1502
MATERIALTool steel
M18x1.5 6H GO/NO-GO thread plug gauge
Internal thread gauge according to PN-ISO 1502:1998
| TECHNICAL DATA | |
|---|---|
| Thread type | ISO metric (M) — fine pitch |
| Thread size | M18x1.5 |
| Thread pitch | 1.5 mm (fine) |
| Tolerance class | 6H |
| Gauge type | GO / NO-GO |
| Material | Tool steel, hardened |
| Hardness | 58-62 HRC |
| Standard | PN-ISO 1502:1998 |
| Manufacturer | Varel |
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 M18x1.5-6H — 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 M18x1.5 6H provides the fastest check of a threaded hole — without a micrometer or calculations. The end GO must enter by hand along the full thread length, while the end NO-GO must stop after no more than 2 turns, counted when unscrewing. GO enters, NO-GO does not — the hole meets class 6H.
Threads in this range are used in load-bearing joints: flanges, bearing supports, and actuator mountings. Reworking an incorrectly machined hole requires boring it out and installing a threaded bushing, so inspection before assembly is less expensive. The fine pitch of 1.5 mm provides a shallower profile and less clearance than the coarse pitch of 2.5 mm. The gauge fits only the thread M18x1.5 — M18 with a 2.5 mm pitch requires a separate gauge. For reference: the internal thread minor diameter M18x1.5 is 16.376 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 M18x1.5 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 internal thread dimensions. It must screw in freely along the full thread length. If it does not enter — the thread is undersized (the workpiece requires rework).
NO-GO end
Marked with a red ring. Checks maximum thread dimensions. It must not screw in more than 2 threads, with turns counted when unscrewing the gauge, not when screwing it in. If it goes farther — the thread is too loose and the part does not meet the tolerance class. For a thread 3 turns long or shorter, the NO-GO end must not pass all the way through.
✓ 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 M18x1.5 thread
Comparison of tolerance classes for an M18x1.5 internal thread
Comparison of classes 4H, 5H, 6H and 7H
Basic pitch diameter D2 for the thread M18x1.5 is 17.026 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 | 17.026 mm | 17.026 – 17.144 mm | 0.118 mm | Precision | |
| 5H | 17.026 mm | 17.026 – 17.176 mm | 0.150 mm | Close | |
| 6H | 17.026 mm | 17.026 – 17.216 mm | 0.190 mm | Standard | THIS PRODUCT |
| 7H | 17.026 mm | 17.026 – 17.262 mm | 0.236 mm | Coarse |
The full range of class 6H for the thread M18x1.5 is 0.190 mm: from 17.026 to 17.216 mm. Class 6H corresponds to a typical nut and a standard machine tap — it is selected for class 6g bolts. Classes 4H and 5H reduce clearance where the thread guides a component; 7H leaves an allowance for electroplating. The values in the table refer to pitch diameter D2, not the tap drill diameter.
Set contents and storage
Set contents and gauge storage
INCLUDED:
| ✓ | M18x1.5 6H GO/NO-GO thread plug gauge |
| ✓ | Size marking on the plug |
STORAGE:
| ✓ | Store in a dry place, in its case |
| ✓ | Protect against dropping — impact damages the thread |
| ✓ | Apply rust-preventive oil periodically |
Frequently asked questions
6H is the most commonly used internal thread tolerance class according to ISO 965-1. The digit 6 specifies the tolerance grade (zone width), and the letter H indicates the tolerance zone position (lower deviation = 0). Class 6H provides a standard fit with class 6g bolts.
The end GO (GO, with the longer thread) must enter freely along the full thread length. The end NO-GO (NO-GO, red) should not screw in more than 2 turns (counted when unscrewing). Both conditions must be met simultaneously for the thread to be considered acceptable according to PN-ISO 1502:1998.
Gauge wear is checked by periodic measurement at intervals based on usage intensity (ISO 1502, clause 7.2.1); the standard specifies neither the number of measurements nor a fixed interval. A worn gauge gives false positive results — the NO-GO end starts entering the thread. The gauge should be verified periodically using setting gauges.
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Shipping
All orders are delivered by courier company GLS. For orders exceeding 369 PLN gross shipping is FREE
| Courier GLS | Przelew24 / Prepayment | 14,76 zł gross | Delivery time 1 working day |
| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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