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Description
ThreadM2 × 0.4
Tolerance class6g
SetGO + NO-GO
StandardISO 1502
Technical specifications of the M2 × 0.4 thread ring gauge
Gauge set specifications according to ISO 1502
| TECHNICAL DATA | |
|---|---|
| Gauge type | GO + NO-GO thread ring gauge set |
| Thread | M2 × 0.4 mm |
| Tolerance class | 6g |
| Nominal diameter (d) | Ø2.000 mm |
| Pitch diameter (d2) | 1.740 mm |
| d2 range for 6g | 1.654 – 1.721 mm |
| Minor diameter (d3) | 1.509 mm |
| Thread pitch (P) | 0.4 mm |
| Thread angle | 60° |
| Material | Tool steel, hardened |
| Hardness | 58–62 HRC |
| Gauge standard | ISO 1502 / DIN 2285 + DIN 2299 |
| Thread standard | ISO 965-1 / DIN 13-1 |
| Reference temperature | 20 °C |
T
GO ring gauge — screwed on by hand along the full bolt thread.
Z
NO-GO ring gauge with a groove in the knurled surface — stops after no more than 2 turns.
The M2-6g engraving on the face of both rings indicates the size and tolerance class of the bolt being inspected.
Limit gauging principle: GO + NO-GO
Gauge for M2 external threads according to ISO 1502
1
The GO ring gauge is screwed on by hand, without force, along the full thread of the M2 x0.4 bolt.
2
The NO-GO ring gauge stops after no more than 2 turns — turns are counted when unscrewing.
3
The GO ring gauge passed, NO-GO stopped — the bolt meets class 6g.
The ring gauge set M2 × 0.4 6g checks an external thread — on a bolt, stud or turned pin. The ring gauge GO must screw on by hand along the full thread length, while the ring gauge NO-GO may advance no more than 2 threads, counted when unscrewing. Only both results together confirm that the thread is neither oversized nor undersized.
Threads of this size are cut on small pins and screws for instruments, optics, and electronic housings. The entire tolerance is within hundredths of a millimeter, so visual assessment is of no use here. The 0.4 mm pitch is the coarse pitch for this diameter: the designation M2 without a specified pitch denotes this thread. For reference: the thread minor diameter M2 × 0.4 is 1.509 mm — this cross section determines the bolt's strength, while the gauge checks the pitch diameter.
The gauge GO has a full thread profile and represents the upper tolerance limit (d2 max = 1.721 mm) — it must screw on by hand over the full length, without a wrench. The gauge NO-GO has a truncated profile and checks the lower limit (d2 min = 1.654 mm); according to ISO 1502 §7 must not engage more than 2 threads.
Thread inspection M2 × 0.4 — class 6g
1 GO gauge
screws on the full length: YES
2 NO-GO gauge
advances max. 2 turns: YES
✓ Conforming thread
class 6g confirmed
Inspection standard: ISO 1502 · Tolerances: ISO 965-1 · Dimensions: ISO 724 / DIN 13-1
✓ Thread acceptable — GO screws onto the full thread, NO-GO stops.
✗ Thread oversized — GO does not screw onto the bolt.
✗ Thread undersized — NO-GO screws on more than 2 turns.
Tolerance classes for an M2 × 0.4 external thread
Comparison according to ISO 965-1
Comparison of classes 4g and 6g
Basic pitch diameter d2 for the thread M2 × 0.4 is 1.740 mm. The deviations in the table are measured downward from this value.
| Class | d2 nominal [mm] | d2 permissible [mm] | Tolerance zone | Application | Status |
|---|---|---|---|---|---|
| 4g | 1.740 mm | 1.679 – 1.721 mm | 0.042 mm | Precision fit | |
| 6g | 1.740 mm | 1.654 – 1.721 mm | 0.067 mm | Standard fit — bolts, fasteners | THIS PRODUCT |
The full range of class 6g is 0.067 mm. Class 6g is the standard for general-purpose bolts and mates with 6H nuts; 4g reduces clearance in guiding joints, while 6e and 8g leave an allowance for electroplating. The table gives pitch diameter d2, not the thread major diameter.
Proper use and calibration
Maintaining gauge accuracy
Usage rules according to ISO 1502
Before measurement, remove chips and oil from the thread. The gauge is screwed on by hand only — a wrench distorts the result and accelerates wear. Reference temperature: 20 °C. Store the set 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:
| ✓ | 1 × GO thread ring gauge — GO, full thread profile |
| ✓ | 1 × NO-GO thread ring gauge — NO-GO, truncated profile |
| ✓ | Tool steel hardened to 58–62 HRC |
| ✓ | Thread and class marking on the circumference of the ring |
Frequently asked questions
The principle of limit gauging requires checking the maximum and minimum material limits. The GO gauge confirms that the thread is not oversized (it screws on over the full length), and the NO-GO gauge confirms that it is not undersized (it does not engage more than 2 turns according to ISO 1502). Using one gauge leaves the other limit unchecked.
No. The pitch diameter of the thread M2 is 1.740 mm, while M2.5 — 2.208 mm; the pitches also differ (0.4 and 0.45 mm). The M2 ring will not screw onto an M2.5 thread, while the M2.5 ring turns freely on M2 and measures nothing.
The thread is nonconforming, if the GO gauge does not screw on over the full length (d2 above 1.721 mm) or the NO-GO gauge engages more than 2 turns (d2 below 1.654 mm). In both cases, the part must be rejected or reworked. Standards: ISO 965-1 (tolerances), ISO 1502 (procedure).
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