When you heat things up, they usually expand at varying rates. This can either be a problem that you need to handle or it can be a tool to solve problems.
Use thermal expansion (or contraction) of materials.
Fit a tight joint together by cooling the inner part to contract, heating the outer part to expand, putting the joint together, and returning to equilibrium.
If thermal expansion is being used, use multiple materials with different coefficients of thermal expansion.
- The basic leaf spring thermostat: (2 metals with different coefficients of expansion are linked so that it bends one way when warmer than nominal and the opposite way when cooler.)