Which tolerance is standard for a 25mm nominal shaft used in precision running fits?

The standard tolerance for a 25mm nominal shaft used in precision running fits is represented by the H8f7 fit. This fit is commonly utilized for situations requiring a close to medium level of precision, where the shaft needs to fit into a hole with minimal clearance yet still allows for smooth operation without excessive tightness.

The "H8" denotes a hole that has a higher level of precision and is suitable for a 25mm nominal size, ensuring that the shaft securely fits without too much interference. The "f7" specifies the tolerance for the shaft itself, which indicates a small amount of allowable negative tolerance. This balance ensures an optimal fit for dynamic applications where parts must slide or rotate freely, as is typically required in precision engineering contexts.

Considering the requirements for precision fits, the other options may not provide the same level of performance or fit quality. For example, other tolerances may be associated with larger clearances or greater allowances for dimension variations, which would not serve well in a precision application like this one. Thus, H8f7 is the most suitable choice for a precision running fit in this scenario.