What component is typically found at the end of service and emergency air lines?

The component that is typically found at the end of service and emergency air lines is known as "glad hands." These are the fittings that connect the air lines from a truck or tractor to the trailer. They are designed to be a secure and reliable connection, ensuring that air flows properly to operate the trailer's braking system. Glad hands also have a simple, user-friendly design that allows for quick attachment and detachment, enhancing convenience and efficiency when connecting or disconnecting trailers.

In the context of the other components: a towing hitch serves as a coupling device for towing trailers, leaf springs are part of the suspension system that helps support vehicle weight and provide a smooth ride, and brake rotors are components of the braking system that work with brake pads to slow down or stop the vehicle. None of these components are used for connecting air lines to a trailer, which highlights the specific and essential role glad hands play in vehicle operation concerning air brakes.