Thread gauges — go/no-go compatibility (d2)

How to use the thread gauge compatibility calculator

Enter the average part diameter limits (D2 for internal threads, d2 for external threads) and the limits of your GO and NO-GO gauges - the calculator will immediately show whether your inspection is calibrated correctly: whether GO will produce false defects and whether NO-GO will miss a defective part.

Two operating modes:

• Ready limits—enter actual values ​​from the caliber certificate or data sheet.
• Double tolerances (Tg + W)—you set the caliber manufacturing tolerance Tg and the wear allowance W, the calculator itself builds the GO and NO-GO limits and checks their compatibility.

Why is the average diameter D2/d2 and not the outer one?

The average diameter is the main parameter of thread interchangeability. It is by this that the nature of the fit is determined: guaranteed clearance or interference. The outer and inner diameters have wider tolerances and do not alone determine compatibility.

Working according to D2/d2 also avoids conflicts when mixing standards: ISO, JIS and GB give different positions of the tolerance fields for the outer diameter, while the average diameter remains an unambiguous parameter.

Typical errors when monitoring thread gauges

False defect. Occurs when the GO gauge is too hard: its upper limit GO_max exceeds the lower part limit D2_min. A good part does not pass through - the batch is sent for rework or written off.

Skip scrap. Occurs when NO-GO is too weak: the lower limit NO-GO_min is lower than the upper limit of the part D2_max. The caliber fits - the part is accepted as suitable, although the average diameter is above the tolerance.

Conflict of standards. The part is designed according to ISO, but the gauge is supplied according to JIS or GB - the GO/NO-GO limits are shifted, and the entire batch control is incorrect.

Frequently Asked Questions

What are Tg and W?Tg - the tolerance for the manufacture of the caliber itself (how accurately its thread is made). W - allowance for wear, applies only to the GO caliber: taking into account wear, the GO is allowed to be slightly “less” than the nominal value.

Is it possible to use one gauge for different thread standards? Only if the D2/d2 limits for both standards are the same. In other cases, there is a risk of false defects or omissions, and it is worth checking before starting a batch with this particular tool.

The caliber does not pass - what to do? First check if there is a conflict of standards. Then check the accuracy class of the caliber (AA, A, B) - different classes give different Tg and W. If a conflict is confirmed, a caliber of the same standard as the part will be required.

Need gauges for metric, imperial or pipe threads? We deliver from the catalog and select according to the drawing.