for temporary engagement in an exposed portion of at least one of the grooves of the worm and a pressure device including a pneumatic piston for moving the mobile device in contact with at least one of the grooves of the worm application_number US 63792103 A description with reference to fig1 and 2 the linear motion device of the present invention marked in its whole with 10 in fig1 comprises a box shaped body 12 for example a regular prism body provided with opposite sidewalls 24 26 and with an upper edge or mouthpiece 20 inside the box shaped body 12 a housing seat of a worm 14 being able to rotate with any suitable means is formed the seat is advantageously obtained in a central position inside the body 12 wherein it is crosswise extended and delimited and in its lower part by the internal side of the base of the same body and sideways by opposite shoulders 16 18 the shoulders 16 18 develop in height for a limited portion while remaining remarkably spaced with their upper end from the edge or mouthpiece 20 of the box shaped body 12 therefore the worm 14 is partially exposed in its.