Tolerance
In engineering, tolerance refers to the permissible deviation from a nominal dimension.
Tolerances play a special role in threads:
- They define how tightly or loosely an internal thread (e.g. nut) fits with an external thread (e.g. screw).
- Tolerance classes are defined in standards (e.g. DIN ISO): e.g. 6H for internal threads, 6g for external threads.
- The letter describes the basis (clearance or interference), the number the accuracy – the smaller the number, the tighter the tolerance.
For taps or dies, the tolerance indicates how the produced thread will turn out. A tap marked 6H cuts an internal thread in the 6H tolerance class.