30 is made of a relative hard but somewhat resilient plastic material polyarylamide with 50 glass fibers admixed such as the product sold under the trade name of ixef 1022 while the wedge 16 is made of die cast zinc when the leg 2 is to be unfolded the top 31 and the corner edge 32 will disengage with a click caused by a relief of a deformation of the rounded top 31 by the corner edge 32 moreover as the surface 25 is slightly rough a certain friction between the corner edge 32 and the surface 25 will together with the force of the spring 19 in the direction r 5 exert a certain further resistance against rotation of the pivot 13 in the leg unfolding direction the resistance against unfolding may be varied by varying the inclination and width of the surface 25 as well as the surface texture and thereby the friction between the surface 25 and corner edge 32 the further the rounded corner edge 32 of the wedge 16 is located past the start of the curvature of the rounded top 31 in the holding position the greater the initial deformation when unfolding and thereby the resistance against unfolding the aforementioned u201c click u201d.