What are the devices called that connect the service and emergency air lines from a truck to a trailer?

The devices that connect the service and emergency air lines from a truck to a trailer are known as glad hands. These are specially designed fittings that create a secure connection between the air lines of the truck and trailer, ensuring that the braking system functions properly. Glad hands allow for easy coupling and uncoupling of air lines, which is crucial for the safe operation of heavy trucks and trailers, as they enable the delivery of compressed air necessary for the trailer’s braking system to operate effectively.

The other options do not accurately describe this specific function. Linkages refer to mechanisms that connect and work together but do not specifically pertain to air line connections. Tow bars are used for towing purposes but are not directly related to the air systems of trucks and trailers. Brake lines typically refer to the lines that carry brake fluid, primarily in hydraulic braking systems, and do not encompass the air connection aspect necessary for trailer brakes.