Abstract: A rotary seamer (1) comprises a seaming turret (2), a seaming station pivotally associated to the seaming turret (2) to set in rotation around its own axis (8) a container (6) to be seamed, a shaft (11) having a first end (13) hinged in the seaming turret (2), a seaming block (9) also called lever, defining a cavity (15) with longitudinal development, shaped complementarily relative to a second end (14) of the shaft (11) in such a way that it can be coupled thereto by inserting the shaft (11) into the cavity (15), and means (16) for anchoring transversely the seaming block (9) to the shaft (11), acting in a predetermined transverse direction (17) in such a way as to create at least one contact surface (20) between shaft (11) and cavity (15), said second end (14) of the shaft (11) and said cavity (15) being so shaped that said contact surface (20) has at least one oblique portion relative to the direction (17) in which said means (16) act.