The support body (12) has a socket (16) with clamping jaws (17,18) between which the guide element (13) is held by tension force. One of the clamping jaws can be fixed and the other resilient. A stop face (19) is provided which fixes the parallel guide of the guide element.Several tension elements (24) can engage on at least the resilient clamping jaw over the longitudinal extension of the support body. The resilient jaw can engage with tension force on the guide element eccentrically in the direction of the guide face of the guide element so that the latter is pressed against the stop face when tensioned.
