Billet Thermostat housing Audi 5 Cyl This Thermostat housing is designed for those who want to run their own radiator hoses with, for example, AN fittings. The thermostat housing is designed so that it should fit bolt on to the block, but give you an M40x1.5 thread for e.g. a hose connection in the desired diameter or with an AN connection. Fits: AAN, ADU, ABY, 3B, D5252T, AEL, AAT, 7A. with more. Does NOT fit original radiator hoses, this is for aftermarket parts. For example, AN connections. Highest processing precision, designed to give the highest flow possible at the transition. O-ring seal between AN coupling and thermostat housing.