Which type of connection is acceptable for joining plastic and steel casings?

The correct answer is based on the compatibility and integrity required for joining different materials, specifically plastic and steel casings in well water systems. A threaded plastic to steel coupling is designed to accommodate the differing characteristics of plastic and steel, providing a reliable seal while allowing for the expansion and contraction that may occur due to temperature changes.

This type of coupling typically features threads that seamlessly fit together, ensuring a secure connection without compromising the integrity of either material. The coupling is specifically engineered to handle the stress of a well environment, where vibrations and pressure fluctuations are common.

Other connection types, such as welded connections, are unsuitable for joining plastic and steel, as welding requires similar material properties for effective bonding. Screwed connections may not provide the necessary seal over time, and bolt connections can be cumbersome and may not allow for the same level of flexibility as a threaded coupling. Hence, using a threaded coupling specifically designed for this purpose ensures a stronger and more reliable connection.