Abstract: A pneumatic expandable shaft having lugs suitable for blocking bobbins mounted on the shaft is described. The shaft comprises in the interior a tube (7) made of resilient material, the tube communicating with the exterior by means of valves (6-15). The valves permit the inflation of the tube by means of compressed air. The shaft has along its surface openings for the passage of lugs (2), the lugs being pushed outwardly under the pneumatic force of the tube (7). When the tube is deflated, the lugs are brought back to their position in the interior of the shaft by the action of springs (14).