CH677632

An apparatus having two slide supports, adjustable with respect to one another, which have attachment surfaces for attaching two holding devices. The balance of the holding devices attached to the attachment surfaces of the slide supports are compensated by having the slide supports each divided into a slide support base plate and an attachment plate with the attachment surface. The attachment plates are connected in a limited adjustable manner with the slide support base plates under spring tension using spring-stressed bolts oriented perpendicular relative to the attachment surfaces. The attachment plate of the first slide support is adjustable in a limited manner through use of an adjustment bolt oriented perpendicular relative to the direction of adjustment of the slide supports on the coordinated slide support base plate. The attachment plate of the second slide support is adjustable in a limited manner relative to the respective slide support base plate through use of an adjustment bolt oriented perpendicular relative to the attachment surface.