Limits and Fits from Deviations

Using deviations

Add the lower and upper deviations to the common nominal size to obtain the hole and shaft limits. Take deviations from the drawing or the applicable standard table. This tool does not convert ISO letters or IT grades into deviations.

Clearance and interference

Subtract the largest shaft from the smallest hole. A zero or positive result gives a clearance fit. If the largest hole does not exceed the smallest shaft, the fit is an interference fit. Overlapping ranges allow both outcomes and give a transition fit. Interference magnitudes are positive while the corresponding hole minus shaft differences are negative.

Example and limits

At a nominal size of 50 mm, hole deviations of 0 and 30 µm and shaft deviations of minus 30 and minus 10 µm give 10 to 60 µm clearance. These are example inputs. The calculation compares dimensional intervals only. It does not establish assembly performance, surface condition or measurement uncertainty.

Reading a transition fit from its limits

Take a common nominal size of 25 mm. Let the hole's lower and upper deviations be 5 and 25 µm and the shaft's be 10 and 20 µm. These are user inputs, not a standard tolerance class. The hole can range from 25.005 to 25.025 mm and the shaft from 25.010 to 25.020 mm. The minimum difference is 5 − 20 = −15 µm and the maximum is 25 − 10 = 15 µm. One assembly can therefore have interference while another has clearance. This is a transition fit.

Subtracting the middle sizes to obtain a single difference does not represent every manufacturing outcome. Compare opposite extreme limits. Also distinguish a signed difference from the magnitude of interference. A negative difference means the shaft can be larger than the hole, not that a physical diameter is negative. Check millimetres versus micrometres when entering deviations and confirm that upper deviations are not below lower ones. This preliminary calculation only compares size intervals. A transition fit does not establish whether hand assembly is possible or predict pressing force. Assembly method, surface condition and operating temperature require separate assessment.

Frequently asked questions

What is the clearance of a hole and shaft fit in millimetres?

For a preliminary example with nominal size 50 mm, hole deviations 0 and 40 µm and shaft deviations -30 and -10 µm, the fit has clearance, ranging from 0.01 to 0.07 mm. Limits are paired to find minimum and maximum clearance, and this dimensional calculation does not establish surface condition or assembly suitability.

Calculate with these values