The difference between a shrink fit and an expansion fit is that in a shrink fit the internal part is cooled to a sufficiently low temperature to reduce its size for assembly, whereas in an expansion fit, the external part is heated sufficiently to increase its size for assembly:

Question

Quizplus · Accepted Answer

in a shrink fit the external part is heated and then cooled to shrink it onto the internal part.in an expansion fit, the internal part is cooled to contract it for assembly; it then expands to form the interference fit.

The Difference Between a Shrink Fit and an Expansion Fit