A unit (1, 1') for forming/advancing at least one pack or at least one portion of a pack, comprising: - a stationary frame (11, 12a, 12b); - a selectively activatable/deactivatable source of power; and - at least one carriage (14a, 14b) operationally coupled with said source of power, movable along a path (13a, 13b) comprising at least one vertical portion (18a, 18b, 19a, 19b), and adapted to convey said at least one pack or said at least one portion of a pack; the unit (1, 1') comprising stopping means fitted to said stationary frame (11, 12a, 12b) and which can be operated: - to leave said carriage (14a, 14b) free to advance along said vertical portion (18a, 18b; 19a, 19b), when said source of power is activated; and - to stop said carriage (14a, 14b) along said vertical portion (18a, 18b; 19a, 19b), when said source of power is, in use, deactivated, wherein said carriage (14a, 14b) comprises a first stop element and said stopping means comprise a second stop element (52, 52'); said stopping means being selectively movable between: - a release configuration in which said first stop element and second stop element (52, 52') are decoupled; and - a stop configuration, in which said first stop element and second stop element (52, 52') are blocked to one another, characterized in that said first stop element is an appendix protruding from said carriage (14a, 14b); said stopping means comprising a first wall, which defines together with a second wall (52, 52') a slot through which said appendix is movable, when said carriage (14a, 14b) is movable along said vertical portion (18a, 18b; 19a, 19b); said second wall (52, 52') defining said second stop element (52, 52') and being selectively movable between: - a closed position, in which it cooperates with said first wall, so as to block said appendix inside said slot; and - an open position, in which it is detached from said first wall, so as to allow said appendix to move along said slot. - a stationary frame (11, 12a, 12b); - a selectively activatable/deactivatable source of power; and - at least one carriage (14a, 14b) operationally coupled with said source of power, movable along a path (13a, 13b) comprising at least one vertical portion (18a, 18b, 19a, 19b), and adapted to convey said at least one pack or said at least one portion of a pack; - to leave said carriage (14a, 14b) free to advance along said vertical portion (18a, 18b; 19a, 19b), when said source of power is activated; and - to stop said carriage (14a, 14b) along said vertical portion (18a, 18b; 19a, 19b), when said source of power is, in use, deactivated, wherein said carriage (14a, 14b) comprises a first stop element and said stopping means comprise a second stop element (52, 52'); - a release configuration in which said first stop element and second stop element (52, 52') are decoupled; and - a stop configuration, in which said first stop element and second stop element (52, 52') are blocked to one another, characterized in that said first stop element is an appendix protruding from said carriage (14a, 14b); - a closed position, in which it cooperates with said first wall, so as to block said appendix inside said slot; and - an open position, in which it is detached from said first wall, so as to allow said appendix to move along said slot.