Final answer:
An expansion joint is used to prevent damage to PVC pipes caused by temperature changes by absorbing thermal expansion and contraction.
Step-by-step explanation:
The type of fitting used to prevent damage to PVC caused by temperature changes is an expansion joint. When PVC pipes are subjected to temperature fluctuations, they can expand and contract. This movement can cause stress on the piping material potentially leading to cracks or breaks. An expansion joint is specifically designed to absorb this thermal expansion and contraction safely without damaging the pipe. Unlike other fittings such as reducers, couplings, or elbows which are used to connect pipes at certain angles or reduce their size, an expansion joint allows for movement due to thermal changes.