Shrink fitting is a method used for making mechanical joints when axles, bushings and similar are to be fitted inside a part with a hole. The hole is then made slightly too small for fitting at even temperature, and so the outer part needs heating up, or the inner part needs cooling down.
Heating up the outer part may take long time, and sometimes heating cannot be made at all because of metallurgical reasons. But cooling down the inner part will not affect the property of the metal, and can be made much faster.
Using liquid nitrogen as a coolant a temperature difference of 200 oC can be achieved. For cooling down the inner part it shall be kept in liquid nitrogen (temp. -196oC), which will make it shrink enough to fit in. The joint will become durable when temperatures are even.
Shrink fitting with liquid nitrogen is an ideal solution for this kind of joints.