Taps - Tolerances

It is a reality of modern manufacturing processes that actual dimensions and target dimensions never match perfectly. Absolute manufacturing accuracy can hardly be achieved in practice and is not necessary in terms of time and cost-efficient production. However, to ensure that the fit of components is not compromised, tolerances must be adhered to. The tolerance specifies where and to what extent the workpiece may deviate from the specified drawing data.

Thread tolerance classes are identified by a number and a letter:

The degree of tolerance is indicated by a number, which in thread cutting is usually in the range between 4 and 7. This number indicates how much the actual value may deviate. In general, the smaller the number, the greater the accuracy.

The tolerance field is identified by a letter that describes where the tolerance is in relation to the nominal dimension or the zero line. For thread tolerances, a distinction is made between internal threads - designated with capital letters G or H - and external threads - designated with lower case letters e, f, g or h. The thread tolerance fields are designed so that external threads are above and internal threads are below the nominal dimension. This ensures that the screw and nut always fit correctly.


Flank diameter tolerance of the internal thread in accordance with DIN ISO 965-1

Tap with special flank diameter tolerance diameter

Flank diameter tolerance of the tap according to DIN EN 22857

Flank diameter tolerance of the reject plug gauge according to DIN ISO 1502

Flank diameter tolerance of the plug gauge according to DIN ISO 1502


Basic size


Tol. class 5 of the internal thread (Tol. unit)


Tolerance of the flank diameter

Representation of the tap tolerances as a diagram

Exact fits in particular are not always the goal when it comes to tolerances. Some treatments, such as thick coatings, can only be implemented if there is sufficient clearance. This is also referred to as oversize. On the other hand, threaded connections with very little play are produced by undersize tolerances.

Tolerance class TapTolerance field nut threadRemarksApplications
4H (DIN 802/1)ISO 14H5HUndersizeThreaded connections with little play
6H (DIN 802/1)ISO 24G5G6HNormalNormal threaded connection
6G (DIN 802/1)ISO 36G7H8HMeasurementThreaded connections with a lot of play
7G (DIN 802/4)7G8GAllowancebefore heat treatment leading to distortion
6H +0,1Measurementgalvanic surface treatment w. Layer thickness ≈ 25μm
6H +0,2Measurementgalvanic surface treatment w. Layer thickness ≈ 50μm