of magnetic attraction creates a tightening torque around the line of rotation 3 the magnetized semi clamp ensures the immobilization of the part 5 on either the worktop or the object 4 the part being wedged between the magnetized semi clamp and the worktop or the object fig4 under the influence of the magnetic force the lever arm 2 ensures the easy separation of the clamp from the surface by swivelling around the line of rotation 3 of the clamp fig2 the line of rotation 3 is at any time the axis of rotation of the device that passes through the one or more contact points between the magnetized surface and the worktop the magnetized surface 1 includes a line that will be called the separating line of poles 6 this line being approximately the perpendicular bisector of the segment bounded by both the center of gravity of south poles and the center of gravity of north poles of magnetization of the surface one finds a lt lt force gt gt of south pole on a side of the separating line of poles as great as the lt lt force gt gt of north pole on the other side of the line the centers of gravity of both north poles and south poles being of the same mass on the magnetized surface 1 the shape of the lever arm 2 is selected so as to make it possible the user to exert either a roughly orthogonal force on the magnetized surface or a torque towards the line of rotation 3 of the magnetized semi clamp this arrangement prevents the slip of the magnetized semi.