A holding means (4) intended to hold a plate-like element (1) to a post (7). The holding means (4) is provided with a peg (41) having different cross-sections (43, 44) formed at two perpendicular coordinates. In a first position of rotation (Figure 3) of the means (4) relative to the first element (2), the peg (41) can be inserted into said element (2), and upon further rotation of the means (Figure 4) to a second position of rotation, the larger cross-section (44) of said peg (41) will clamp the holding means firmly against surfaces (23, 24) formed in said first element (2).