A linear motion device (10) associated to a worm (14) including a body (12) internally provided with a housing seat for partially receiving a worm having a plurality of grooves, a mobile device (52) for temporary engagement in an exposed portion of at least one of the grooves (54) of the worm, and a pressure device (40) including a pneumatic piston for moving the mobile device in contact with at least one of the grooves of the worm.