Which letter indicates the medium wall thickness of copper tubing?

The designation for the medium wall thickness of copper tubing is represented by the letter "M." In the context of copper tubing, different wall thicknesses are indicated by specific letters. "K" denotes heavy wall tubing, which has the thickest walls and is typically used for underground installations due to its durability. "L" represents thin wall tubing, which is used for applications that require lightweight piping and lower pressures. "M" is the correct choice because it indicates a medium wall thickness, falling between "K" and "L." The letter "H" does not correspond to any standard copper tubing thickness designation. Understanding these distinctions is essential for selecting the appropriate tubing type for plumbing applications based on pressure requirements and installation conditions.