A press fit illustrates one method to assemble mating parts … to make a larger metal peg fit into
a slightly too small hole and hold it in place.

If we make an assembly of parts using this principle……it is called a press or interference fit.

It just takes the application of force between the two parts to join them together …….. Any of you
who are backyard mechanics have probably used this technique. Sometimes with a hammer to
“persuade” the peg into the hole or a pulley onto a shaft. The force used makes the peg contract
and the mating hole to enlarge. Just a little. A hydraulic press can use a lot more force when
the design requires it.

The resulting residual stresses hold the assembly together; the hole has a residual tensile
stress and the peg has a residual compressive stress.