Abstract: A versatile knockdown fixture includes datum members each of which is provided with at least two intersecting grooves, which are located on the side of mating faces and form, after the mating faces have been joined, unified spaces. At the intersection of the grooves, there is provided an annular recess where there is a sleeve with radial holes in its side. A cylindrical key is secured by an indent made at one of its ends in each hole, which key fits the space with a guaranteed interference. Within the area of contact with the key, the groove has a trapezoid cross section and a depth greater than one half of the diameter of the key.