This tube is the long metal tube that goes under your bus from front to rear to guide the generated heat of your heat exchangers to the front cabin. This tube is indispensable for a good working heater system in ANY bus made between 55 and 72. Fits split and early bay windows, all models from deluxe, panels, pick ups and trucks. If not rusted out, many times this tube is missing or totally dented. We offer the perfect replacement restoration product here! We supply as well the insulation that originally covers the heating tube system .You can find it under BBT ref 1098-500