CLAIMS 1. Screwdriver (1) or key with dynamometric property in order to protect a screw, a bolt or similar threaded fastening element against torque overload during fastening, whereby the screwdriver (1) has a shank part (2) for imparting torque, and a engagement part (3) with means for engaging a screw, whereby the shank part (2) and the engagement part (3) are interconnected by an intermediate material part (4) which is designed such that it will break when a predefined torque is present between the shank part (2) and the engagement part (3). 2. Screwdriver (1) as defined in claims 1, wherein the shank part (2), the intermediate material (4) part and the engagement part (3) are molded in one piece. 3. Screwdriver (1) as defined in claims 1 or 2, whereby the shank part (2) is rod shaped with an engagement part (3) and an intermediate part (4) at each end. 4. Screwdriver (1) as claimed in claim 1, whereby each of three or more arms circumferentialy spaced in a plane and departing from a common center part form a shank part (2), whereby an engagement part (3) is provided at the end of each shank part (2). 5. Screwdriver (1) as claimed in claim 3 or 4, whereby the intermediate material part (4) of each arm is designed to break at the same torque load. 6. Screwdriver (1) as claimed in one of the above claims and whereby the shank part (2) is facetted to allow easy grip by the users hands and fingers. 7. Screwdriver (1) as claimed in claims 1, 2 or 3 whereby the shank part (2) is designed to fit into a standard screwdriver as an exchangeable bit. 8. Screwdriver (1) as claimed in one of the above claims whereby the shank part (2) has a visual indication of the maximum torque load, which can be applied between the shank part (2) and the engagement part (3) before the intermediate part (4) breaks. 9. Screw (5) with a threaded part (6) and an unthreaded head part (7), whereby the head part (7) extends into a shank part (2) and where the shank part (2) and the head part (7) are interconnected by an intermediate material part (4) which is designed such that it will break when a predefined torque is present between the shank part (2) and the head part (7) of the screw (5). 10. Screw (5) as claimed in claim 9, whereby the head part (7) of the screw has engagement parts (9) for engagement with a screwdriver. 11. Screw (5) as claimed in claim 9, whereby the threaded part (6), the unthreaded head part (7), the intermediate part (4) and the shank part (2) are molded in one piece. 12. Screw (5) as claimed in claim 9, whereby the shank part (2) is rod shaped with an engagement part (3) and an intermediate part (4) at each end. 13. Screw (5) as claimed in claim 9, whereby each of three or more arms circumferentialy spaced in a plane and departing from a common centerpart form a shank part (2), whereby a threaded part (6) is provided at the end of each shank part (2). 14. Screw (5) as claimed in claim 9-13, whereby the intermediate material part (4) of each arm is designed to break at the same torque load. 15. Screw (5) as claimed in claim 9-14 whereby the shank part (2) is facetted to allow easy grip by the users hands and fingers. 16. Screw (5) as claimed in claim 9-11 whereby the shank part (2) is designed to fit into a standard screwdriver as an exchangeable bit. 17. Screw (5) as claimed in one of claims 9-16 where the shank part (2) has a visual indication of the maximum torque load, which can be applied between the shank part (2) and the threaded part (6) before the intermediate part (4) breaks.CLAIMS 1. Screwdriver (1) or key with dynamometric property in order to protect a screw, a bolt or similar threaded fastening element against torque overload during fastening, whereby the screwdriver (1) has a shank part (2) for imparting torque, and an engagement part (3) with means for engaging a screw, whereby the shank part (2) and the engagement part (3) are interconnected by an intermediate material part (4) which is designed such that it will break when a predefined torque is present between the shank part (2) and the engagement part (3). 2. Screwdriver (1) as defined in claims 1, wherein the shank part (2), the intermediate material (4) part and the engagement part (3) are molded in one piece. Screwdriver (1) as defined in claims 1 or 2, whereby the shank part (2) is rod shaped with an engagement part (3) and an intermediate part (4) at each end. 4. Screwdriver (1) as claimed in claim 1, whereby each of three or more arms circumferentially spaced in a plane and departing from a common center part form a shank part (2), whereby an engagement part (3) is provided at the end of each shank part (2). 5. Screwdriver (1) as claimed in claim 3 or 4, whereby the intermediate material part (4) of each arm is designed to break at the same torque load. 6. Screwdriver (1) as claimed in one of the above claims and whereby the shank part (2) is facetted to allow easy grip by the users hands and fingers. 7. Screwdriver (1) as claimed in claims 1, 2 or 3 whereby the shank part (2) is designed to fit into a standard screwdriver as an exchangeable bit. 8. Screwdriver (1) as claimed in one of the above claims whereby the shank part (2) has a visual indication of the maximum torque load, which can be applied between the shank part (2) and the engagement part (3) before the intermediate part (4) breaks. 9. Screw (5) with a threaded part (6) and an unthreaded head part (7), whereby the head part (7) extends into a shank part (2) and where the shank part (2) and the head part ( 7) are interconnected by an intermediate material part (4) which is designed such that it will break when a predefined torque is present between the shank part (2) and the head part (7) of the screw (5). 10. Screw (5) as claimed in claim 9, whereby the head part (7) of the screw has engagement parts (9) for engagement with a screwdriver. 11. Screw (5) as claimed in claim 9, whereby the threaded part (6), the unthreaded head part (7), the intermediate part (4) and the shank part (2) are molded in one piece. 12. Screw (5) as claimed in claim 9, whereby the shank part (2) is rod shaped with an engagement part (3) and an intermediate part (4) at each end. 13. Screw (5) as claimed in claim 9, whereby each of three or more arms circumferentially spaced in a plane and departing from a common centerpart form a shank part (2), whereby a threaded part (6) is provided at the end of each shank part (2). 14. Screw (5) as claimed in claim 9-13, whereby the intermediate material part (4) of each arm is designed to break at the same torque load. 15. Screw (5) as claimed in claim 9-14 whereby the shank part (2) is facetted to allow easy grip by the users hands and fingers. 16. Screw (5) as claimed in claim 9-11 whereby the shank part (2) is designed to fit into a standard screwdriver as an exchangeable bit. 17. Screw (5) as claimed in one of claims 9-16 where the shank part (2) has a visual indication of the maximum torque load, which can be applied between the shank part (2) and the threaded part (6) before the intermediate part (4) breaks.