Abstract: The connection device between a tube end plate and a header box of a heat exchanger comprises at least one clamp bearing underneath bottom of a peripheral groove of the tube end plate and on top of a peripheral bearing flange of the header box by means of lugs separated by notches. The clamp is preformed for defining upper lugs and lower lugs, said upper end lower lugs being separated by a measure for which a gasket mounted between the tube end plate and the header box is deformed in a regular manner, and said clamp having at least one lower lug of a greater length than width of the bottom of the peripheral groove of the tube end plate and being bent over beyond said bottom.