intermediate crank lever 54 and plate 12 it is provided with a rectangular recess 61 whose frontal vertical boundary edge 62 is disposed so that locking lever 58 is moved by the pin 50 carried on lever arm 57 into the locking positon shown in fig3 as soon as release button 4 is brought after a release operation and by tension spring 43 acting on guide levers 32 and 33 into its locking position which at the same time is its rest position during this operation crank lever 54 executes a pivotal motion in the clockwise direction as viewed in fig3 and 6 which results in its final phase in a counterclockwise pivotal motion of locking lever 58 since pin 50 comes into contact with edge 62 of recess 61 locking lever 58 can be blocked in its locking position by means of two locking mechanisms which are independent of each other one or the first of these mechanisms or means comprises a tongue 63 which is angled into the plane of crank lever 54 and spaced from pivot pin 59 by a distance which is about six times greater than that of locking tongue 60 and in whose outer path of motion a two armed hinged armature 64 of an electromagnet 65 is provided the coil yoke 67 having the shape of an angle plate and carrying the coil 66 and the coil core is screwed to the inside of plate 11 by means of screws 68 at the respective location plate 11 is provided with a corresponding recess 69 at the side of vertical yoke plate 67 which is remote from the solenoid a supporting angle 70 with a spring eye 71 is secured from which a tension spring 72 is suspended the other end.