Various embodiments include a structure for positioning a tool on an elongated recess of a workpiece, wherein the elongated recess extends along a first longitudinal axis and has end surfaces on two end faces. The structure may include a plate having a cutout extending along an axis; a centering device; and a clamping device fixedly connected to the plate and the centering device. The cutout, when the second longitudinal axis is aligned parallel to the first longitudinal axis, enframes the elongated recess. The centering device includes a centering jaw movable within the cutout along the second longitudinal axis and also movable into and out of the elongated recess. The clamping device, on the side of the plate facing the elongated recess, includes clamping jaws movable along the second longitudinal axis to come into mechanical contact with one of the end surfaces of the end faces of the elongated recess.