Which of the following materials is NOT typically used for water piping fittings?

Wood is not typically used for water piping fittings due to its inherent characteristics. While wood can be used in certain applications, it is not suitable for plumbing systems that require durability and resistance to water damage. Unlike metals such as copper and steel, which are robust and provide excellent resistance to corrosion, or plastic, which is lightweight and flexible, wood can absorb moisture, swell, and deteriorate over time. This susceptibility to decay makes it an impractical choice for fittings in water systems, where maintaining a watertight seal is crucial to prevent leaks and potential structural damage.