M drawings are used to indicate the size and route of which of the following?

M drawings are specialized documents used in the construction and engineering fields to represent various system layouts and specifications. In this context, they specifically indicate the size and route of HVAC (Heating, Ventilation, and Air Conditioning) system ducts. These drawings detail important information, such as the dimensions of the ducts, the layout of the system, and the required clearances and connections to other components.

Using M drawings for HVAC systems allows for clear communication among architects, engineers, and contractors, ensuring that the air handling components are installed correctly and function efficiently. This is crucial for maintaining climate control and indoor air quality within a building.

Other options, while related to infrastructure and utilities, do not correspond to the specific function of M drawings as they pertain to the HVAC ductwork. Electrical wiring typically uses different drawing standards (such as E drawings), and sanitary sewer lines utilize their own set of standards for plumbing systems. Therefore, the use of M drawings is uniquely associated with HVAC systems.