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Description
ThreadM3 × 0.5
Tolerance class6g
TypeGO
Hardness58–62 HRC
Technical specifications of the M3 × 0.5 thread ring gauge
Gauge specifications according to ISO 965-1
| Technical data | |
|---|---|
| Gauge type | GO thread ring gauge |
| Thread | M3 × 0.5 mm |
| Nominal diameter | Ø3.000 mm |
| Pitch diameter (d2) | 2.675 mm |
| Thread pitch | 0.5 mm |
| Tolerance class | 6g |
| Material | Tool steel, hardened |
| Hardness | 58–62 HRC |
| Standard | ISO 965-1 / DIN 13 |
| Manufacturer | Varel |
Operating principle of the GO gauge
Gauge for M3 external threads
GO ring gauge GO M3 6g checks whether the external thread is oversized — it must screw on by hand along the full length. This is a single-limit check: it detects excess material but will not detect an undersized thread. That requires the ring gauge NO-GO, ordered separately: it may screw onto the thread no more than 2 threads, counted when unscrewing.
Screws and bolts of this size are installed in electronics, optics, and small instruments, where tightening torque is measured in fractions of a newton-meter. A slightly oversized thread jams in the nut before the assembler can feel it. The 0.5 mm pitch is the coarse pitch for this diameter: the designation M3 without a specified pitch denotes this thread. For reference: the thread minor diameter M3 is 2.387 mm — this cross section determines the bolt's strength, while the gauge checks the pitch diameter.
The GO gauge checks the maximum material limit of the external thread, checking pitch diameter, pitch and thread profile simultaneously. If the GO gauge does not screw onto the thread — the part is nonconforming (thread oversized, out of tolerance). Complete thread inspection also requires a gauge NO-GO, which checks the minimum material limit.
Tolerance classes for an M3 × 0.5 external thread
Comparison of classes according to ISO 965-1
Comparison of classes 4g, 6g, and 6e
Basic pitch diameter d2 for the thread M3 is 2.675 mm. The deviations in the table are measured downward from this value.
| Class | d2 nominal [mm] | d2 permissible [mm] | Tolerance zone | Application | Status |
|---|---|---|---|---|---|
| 4g | 2.675 mm | 2.607 – 2.655 mm | 0.048 mm | Precision fit | |
| 6g | 2.675 mm | 2.580 – 2.655 mm | 0.075 mm | Standard fit (bolts) | THIS PRODUCT |
| 6e | 2.675 mm | 2.550 – 2.625 mm | 0.075 mm | Clearance fit (coatings) |
The full range of class 6g for the thread M3 is 0.075 mm — less than the thickness of a sheet of paper: from 2.580 to 2.655 mm. Class 6g is the standard for general-purpose bolts — it mates with 6H nuts. Classes 4g and 5g reduce clearance in guiding joints, while 6e and 8g leave room for electroplating. The values in the table are pitch diameter d2, measured at half the profile height, not the thread major diameter.
Thread inspection process
Correct use of GO/NO-GO gauges
Thread inspection M3 6g
1 GO gauge
screws on: YES
2 NO-GO gauge
screws on: NO — max. 2 turns
✓ Conforming thread
class: 6g OK
Both conditions must be met simultaneously. Standard: ISO 965-1
Usage guidelines
Proper storage and use
Store the gauge in a dry place, protected with rust-preventive oil. Before measurement, remove chips and burrs from the thread being inspected. Screw the gauge on by hand — never use wrenches or force. The calibration interval is determined by the user based on usage intensity — ISO 1502 (clause 7.2.1) requires periodic gauge measurement but specifies neither the interval nor the number of measurements.
Varel gauge features:
| ✓ | Alloy tool steel hardened to 58–62 HRC |
| ✓ | Ground thread profiles for high accuracy |
| ✓ | Thread, tolerance class and type (GO) marked on the ring |
| ✓ | Compliance with ISO 965-1 / DIN 13 |
Frequently asked questions
The GO thread ring gauge is used to inspect M3 external threads of tolerance class 6g. It verifies that the pitch diameter, pitch and thread profile are within permissible limits. The gauge should screw freely onto the full length of the thread being inspected.
The GO gauge checks the maximum material limit — it must screw onto the thread. The NO-GO gauge checks the minimum limit — it should not screw on more than 2 turns. Both gauges are required for complete inspection of an M3 6g thread.
ISO 1502 (clause 7.2.1) requires gauge wear to be checked by periodic measurement at intervals based on usage intensity, but specifies neither the interval nor the number of measurements — these are determined by the user as part of measuring equipment control. Calibration is performed by an accredited metrology laboratory. Between calibrations, it is advisable to check the gauge using a setting plug gauge.
Product accessories
Die M3 HSSE INOX 6g DIN 22 568 Fanar
Reference: 0000007075 In stock > 10 items
€13.42
€16.51 brutto
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| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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