of two parts a stationary workpiece receiving element 23 secured to the stationary bracket 10 and a movable workpiece receiving element 25 received in a guide 24 formed as an oblong hole the movable workpiece receiving element 25 is releasably locked in the guide 24 by a handle 26 the stationary and the movable workpiece receiving elements 23 25 are provided each with a supporting plate 27 or 28 a contoured supporting plate 29 or 30 and a congruent clamping plate 31 or 32 the contoured supporting plate 30 is shaped as to overlap the contoured supporting plate 29 for forming an uninterrupted support for the workpiece 6 at any adjusted position of the movable workpiece receiving element 25 in order to prevent a step at the overlapping the contoured supporting plates 29 30 are cut for example from sheet material having a thickness of 0 5 mm according to fig6 the clamping plates 31 and 32 are movably arranged by means of levers 35 and 36 operated by air cylinders 33 and 34 the air cylinder 33 is stationarily fixed to the bracket 10 while the air cylinder 34 is adjustably connected to the movable workpiece receiving element 25 received in the guide 24 for adjustment purposes the movable workpiece receiving element 25 is installed with a handle 37 the position.