This heat muff can be used for either cabin heat, carb heat, or both; as there are two 2″ outlets and one 2″ inlet. Its design used forced air through the muff, combined with an interior baffle which slows down the air flow increasing the heat output. Its split clamshell design allows it to be mounted over any 12″ straight section of -1/34 exhaust pipe. The offset end flanges allow it to be mounted under a close fitting cow.. Made of 6061 and 5052 aluminum weight with clamps 12 oz. Diameter 3″, length 11″