Horn assembly adapted to be rotatably arranged in a housing (3) of a rotary ultrasonic sealer, and comprising a hollow shaft (1) having a longitudinal axis (2) and a horn (8) arranged coaxially in the hollow shaft (1) and connected to a converter (6) and preferably also a booster (7). The horn (8) is provided with a peripheral sealing area (13) outside an axial end (13) of the hollow shaft (1). The horn (8) is connected to the hollow shaft (1) by means of at least one annular, metallic support (11) extending radially outward from an outer face (14) of the horn (8) and axially acting retaining means so as to fixedly retain the horn (8) in the hollow shaft (1). The at least one annular support (11) is corrugated in cross section such that at least two grooves and one ridge arranged there between are provided between the inner face (10) of the hollow shaft (1) and the outer face (14) of the horn (8). The at least one support (11) comprises at its outer circumference a conical surface (26) adapted to cooperate with a corresponding conical surface (27) for centering the support (11) with respect to the hollow shaft (1).