A transfer drum (17; 25) to transfer objects along a circular path; the transfer drum (17; 25) comprises: a cylindrical support body (18; 26), which is mounted rotatable around a first rotation axis (19; 27); at least one holding head (20; 28), which is mounted rotatable on the support body (18; 26) so as to rotate, relative to the support body (18; 26), around a second rotation axis (21; 29); a cam, which is arranged inside the support body (18; 26) and remains still when the support body (18; 26) rotates around the first rotation axis (19; 27); and an actuator device, which is carried by the support body (18; 26), comprises a cam follower roller engaging the cam, and controls the rotation of the holding head (20; 28) around the second rotation axis (21; 29); wherein the rotation of the support body (18; 26) around the first rotation axis (19; 27) cyclically moves the holding head (20; 28) along a work path, which extends between an input station, where the holding head (20; 28) receives an object, and an output station, where the holding head (20; 28) releases the object, and along a return path, which extends between the output station and the input station; the transfer drum (17; 25) is characterized in that: the cam comprises at least a first portion, which is designed to cause the holding head (20; 28) to move with a first law of rotation motion around the second rotation axis (21; 29), and a second portion, which is designed to cause the holding head (20; 28) to move with a second law of rotation motion around the second rotation axis (21; 29), which is different from the first law of rotation motion and is at least partially alternative to the first law of rotation motion; and the cam is designed to be rotated around the first rotation axis (19; 27), when the support body (18; 26) is still due to a standstill of the machine during which a format change is carried out, so as to place the first portion at least partly at the work path and the second portion at least partly at the return path or vice versa so as to modify the law of rotation motion around the second rotation axis (21; 29) that the cam causes upon the holding head (20; 28) along the work path. a cylindrical support body (18; 26), which is mounted rotatable around a first rotation axis (19; 27); at least one holding head (20; 28), which is mounted rotatable on the support body (18; 26) so as to rotate, relative to the support body (18; 26), around a second rotation axis (21; 29); a cam, which is arranged inside the support body (18; 26) and remains still when the support body (18; 26) rotates around the first rotation axis (19; 27); and an actuator device, which is carried by the support body (18; 26), comprises a cam follower roller engaging the cam, and controls the rotation of the holding head (20; 28) around the second rotation axis (21; 29); wherein the rotation of the support body (18; 26) around the first rotation axis (19; 27) cyclically moves the holding head (20; 28) along a work path, which extends between an input station, where the holding head (20; 28) receives an object, and an output station, where the holding head (20; 28) releases the object, and along a return path, which extends between the output station and the input station; the transfer drum (17; 25) is characterized in that: the cam comprises at least a first portion, which is designed to cause the holding head (20; 28) to move with a first law of rotation motion around the second rotation axis (21; 29), and a second portion, which is designed to cause the holding head (20; 28) to move with a second law of rotation motion around the second rotation axis (21; 29), which is different from the first law of rotation motion and is at least partially alternative to the first law of rotation motion; and the cam is designed to be rotated around the first rotation axis (19; 27), when the support body (18; 26) is still due to a standstill of the machine during which a format change is carried out, so as to place the first portion at least partly at the work path and the second portion at least partly at the return path or vice versa so as to modify the law of rotation motion around the second rotation axis (21; 29) that the cam causes upon the holding head (20; 28) along the work path. the cam comprises at least a first portion, which is designed to cause the holding head (20; 28) to move with a first law of rotation motion around the second rotation axis (21; 29), and a second portion, which is designed to cause the holding head (20; 28) to move with a second law of rotation motion around the second rotation axis (21; 29), which is different from the first law of rotation motion and is at least partially alternative to the first law of rotation motion; and the cam is designed to be rotated around the first rotation axis (19; 27), when the support body (18; 26) is still due to a standstill of the machine during which a format change is carried out, so as to place the first portion at least partly at the work path and the second portion at least partly at the return path or vice versa so as to modify the law of rotation motion around the second rotation axis (21; 29) that the cam causes upon the holding head (20; 28) along the work path.