at the top and an operating surface 38 at the bottom the angle of conicity between these marginal beading surfaces is approximately 90 u00b0 so that in axial section these surfaces are respectively 45 u00b0 to the plane of rotation of the rotating plate 12 in the assembled position as per fig4 the inner marginal beading 34 of the retaining ring 20 extends beneath the outer marginal beading 26 of the annular wall 24 with the retaining surface 36 resting over a large area on the supporting surface 30 of the outer marginal beading 26 the relative dimensions between the top plate 12 and the retaining ring 20 are chosen such that the retaining ring 20 rests directly on the outer portion of the top surface of the top plate 12 and the marginal beading 34 of the retaining ring 20 clamps said retaining ring and holds it firmly against the marginal beading 26 of the top plate 12 in order to dismantle the turntable 10 the retaining ring 20 is lifted off the bottom plate 16 by its outer edge in the process the wedge effect means that the inner marginal beading 34 of the retaining ring 20 causes the annular wall 24 to swing inwards with the deformation taking place essentially in the articulation zone 28 and the adjacent portion of the annular wall 24 the marginal beading 26 is.