The rotating cylinder comprises: an elongated inner core (12) which is substantially rigid and an interchangeable sleeve (45) which is fitted onto the core; the sleeve is axially and angularly constrained to said core and is provided on its external surface with a raised pattern. The internal surface of the interchangeable sleeve and the external surface of the inner core are conical surfaces which are mutually complementary; axial and angular locking of the interchangeable sleeve and the inner core is achieved by the friction between the conical surfaces which are forced axially one onto the other.