When installed vertically, PEX and PEX-AL-PEX must be supported at the base of each story with a mid-story ________.

When PEX and PEX-AL-PEX are installed vertically, it is essential for proper support and alignment throughout the plumbing system. Mid-story guides are specifically designed to assist in managing the expansion and contraction of these flexible piping materials, helping to maintain their position and prevent sagging or undue stress on the joints and connections.

Using guides at mid-story points allows the piping to move slightly due to thermal changes, assuring that the pipes do not become overly restricted or damaged. This support mechanism is crucial for ensuring long-term reliability and efficiency in a plumbing system. While clamps, brackets, and supports can provide various forms of stabilization, the term "guide" specifically emphasizes the function of allowing movement while still directing the orientation and positioning of the piping, making it the most appropriate choice in this context.