Star wheel for a rotary packing machine for containers (50, 52), the star wheel comprising: - a shaft that extends vertically about a main axis and that is driven by a rotary movement about said main axis; - a movable assembly, which comprises: - a frame fixed to said shaft; - a plurality of pairs of arms (102a-d), each comprising two arms (104a-b), each comprising a distal end and a proximal end and hinge mounted on the frame about a vertical rotation axis, where the arms (104a-b) of each pair of arms (102 a-d) are mobile between an open position and a closed position, and vice versa; - for each pair of arms (102a-d), an activation mechanism which has an activation pad mobile between a first limit position and a second limit position, where, in the first limit position, the activation mechanism positions the arms (104a-b) of said pair of arms (102a-d) in the open position and where, in the second limit position, the activation mechanism positions the arms (104a-b) of said pair of arms (102a-d) in the closed position; - a cam, which is fixed relative to the movable assembly and has a guide surface, where the shape of the guide surface is such that each activation pad follows the guide surface in order to successively transition from the first limit position to the second limit position, and vice versa said star wheel being characterized in that the movable assembly comprises: - an adjustment mechanism, which moves the vertical rotation axis of each arm (104a-b) between a first position and a second position, and vice versa; and - a locking mechanism, which locks the position of the vertical rotation axis of each arm (104a-b) between the first position and the second position. - a shaft that extends vertically about a main axis and that is driven by a rotary movement about said main axis; - a movable assembly, which comprises: - a frame fixed to said shaft; - a plurality of pairs of arms (102a-d), each comprising two arms (104a-b), each comprising a distal end and a proximal end and hinge mounted on the frame about a vertical rotation axis, where the arms (104a-b) of each pair of arms (102 a-d) are mobile between an open position and a closed position, and vice versa; - for each pair of arms (102a-d), an activation mechanism which has an activation pad mobile between a first limit position and a second limit position, where, in the first limit position, the activation mechanism positions the arms (104a-b) of said pair of arms (102a-d) in the open position and where, in the second limit position, the activation mechanism positions the arms (104a-b) of said pair of arms (102a-d) in the closed position; - a cam, which is fixed relative to the movable assembly and has a guide surface, where the shape of the guide surface is such that each activation pad follows the guide surface in order to successively transition from the first limit position to the second limit position, and vice versa - a frame fixed to said shaft; - a plurality of pairs of arms (102a-d), each comprising two arms (104a-b), each comprising a distal end and a proximal end and hinge mounted on the frame about a vertical rotation axis, where the arms (104a-b) of each pair of arms (102 a-d) are mobile between an open position and a closed position, and vice versa; - for each pair of arms (102a-d), an activation mechanism which has an activation pad mobile between a first limit position and a second limit position, where, in the first limit position, the activation mechanism positions the arms (104a-b) of said pair of arms (102a-d) in the open position and where, in the second limit position, the activation mechanism positions the arms (104a-b) of said pair of arms (102a-d) in the closed position; - a cam, which is fixed relative to the movable assembly and has a guide surface, where the shape of the guide surface is such that each activation pad follows the guide surface in order to successively transition from the first limit position to the second limit position, and vice versa - an adjustment mechanism, which moves the vertical rotation axis of each arm (104a-b) between a first position and a second position, and vice versa; and - a locking mechanism, which locks the position of the vertical rotation axis of each arm (104a-b) between the first position and the second position.