Century 15Ft Truck Trailer Power Air Brake Lines Stay Flexible to -40&deg;F 1/2" Brass Fittings Each Set Contains Color Coded Hose Assemblies: A Blue Service Line and a Red Emergency Line The Service Line (Blue Hose) carries air that is controlled by engaging the foot brake or trailer hand brake. The Emergency Line (Red Hose) supplies air to the trailer air tanks and to the emergency brakes in the event of loss of air in the system. Our Hose Retains Coil Memory and Flexibility at Temperatures Down to -40F (-40C). 12 Galvanized Steel Spring Strain Reliefs prevent excess bending at connection ends