Which type of copper cannot be used on gas lines?

Type M copper is typically not suitable for use on gas lines due to its thinner walls compared to other types of copper, which reduces its strength and structural integrity. Type M copper is designed primarily for low-pressure applications such as potable water systems and is not appropriate for the demands and regulations surrounding gas transport.

In contrast, Type K and Type L copper possess thicker walls, providing greater durability and strength, making them more capable of withstanding the pressures and potential hazards associated with transporting gas. Type D, while not commonly referenced, could be interpreted as a specification that does not meet the required standards for gas piping, further positioning Type M as the unsuitable choice in this context.

The choice of materials for gas lines is critical for safety and compliance with local plumbing codes, which emphasize the necessity for using appropriate types of copper that can handle the specific pressures involved in gas distribution.