A traction unit (1), particularly for packaging machines, comprising means for moving at least one grip element (2), which can move along a predefined closed path (3) and has at least two pairs of teeth (4a, 4b) which protrude substantially at right angles from the closed path (3), for the clamping of products (5) to be packaged and their traction along a portion of the closed path (3); the mutual transverse arrangement of the pairs of teeth (4a, 4b) being configurable by means of an adjustment device (6) which is located substantially outside the closed path (3), the movement means being located substantially inside the closed path (3).