Abstract: A heat exchanger (2) comprises an end tank (6) defining therein a fluid inlet (16) through which, in use, fluid enters the heat exchanger, and a fluid outlet (20) through which, in use, fluid leaves the heat exchanger (2), a plurality of heat exchange tubes (8) having end portions (10) at which the heat exchange tubes are connected to said end tank (6), a plurality of heat exchange fins (12) connected to the heat exchange tubes (8), a plurality of stubs (28) provided on said end tank (6) extending outwardly therefrom and defining passageways into said end tank, said heat exchange tube end portions (10) being dimensioned to receive said stubs (28), wherein the stubs (28) are each provided with two axially spaced annular grooves (29) on the outer surface thereof, a sealing "O"-ring (30) being seated in each annular groove (29) to provide a seal between the heat exchange tubes (8) and stubs (28).