referring now to the figures of the drawings in detail and first , particularly , to fig1 and 3 thereof , there is seen a ring part 1 which is constructed to be u - shaped in its cross - section . two u - limbs 2 and 3 form an outer and an inner peripheral wall , which form an annular chamber together with a base 6 of the u - shaped ring part 1 . this annular chamber is filled out with a mixture , in which concrete is contained and which forms a concrete ring 7 after hardening . several sockets 8 protruding into the annular chamber between the u - limbs 2 and 3 formed integrally at the base 6 are provided to be distributed around the periphery of the u - shaped ring part 1 . the sockets 8 have free ends 9 at which a receiving opening 10 for a reinforcing ring 11 is formed . this reinforcing ring 11 is inserted into the receiving opening 10 of the sockets 8 before the filling out of the u - shaped ring part 1 , so that it is surrounded by the casting mass during filling out of the u - shaped ring part 1 and imparts a higher strength to the concrete casting ring 7 after hardening thereof . support ribs 30 are disposed at outer surfaces of the u - limbs 2 and 3 in order to sufficiently support the u - limbs 2 and 3 against pressure acting thereon during filling in of the casting mass . projections 12 , which axially secure the concrete ring in the ring part 1 and form undercuts , are formed at inner surfaces of the u - limbs 2 and 3 , although retaining straps 32 could be used . according to fig2 the ring parts 1 can be stacked one above the other . the stacking can take place before or after the filling out of the annular chambers of the ring parts 1 . a pouring - in opening 31 is provided at one or more locations of the outer and / or inner u - limbs 2 and 3 in order to be able to stack the ring parts 1 unfilled . the casting mass can be introduced into the annular chamber in the stacked state of the u - shaped ring parts 1 by way of this pouring - in opening . respective bead - shaped depressions 14 are impressed at free edges 13 of the u - limbs 2 and 3 in order to increase stack rigidity . protrusions 15 lying at the height of the diameter of the u - limbs 2 and 3 are formed on at an outer surface of the base 6 opposite the depressions . during stacking of the ring parts 1 one on the other , these protrusions respectively engage in the bead - shaped depressions 14 of the ring part 1 lying thereunder and thus secure the u - shaped ring parts 1 stacked one on the other against slipping . the ring parts 1 form so - called lost casting moulds and separate , reusable casting moulds are accordingly superfluous . therefore even during casting of the individual concrete rings 7 it is not necessary to wait out a hardening time in order to have the casting mould available again . due to the stackability of the ring parts 1 , a considerably smaller storage area is needed for storage which is necessary for hardening of the cast concrete rings 7 of the ring parts 1 . this also applies to a possible stocking of the concrete rings 7 . a connecting device in the form of a radially outwardly facing connecting flange 16 is furthermore formed on at the ring part 1 . the ring part 1 can be fastened to a washing solution container 17 of a washing machine through the use of this connecting flange 16 . one possible mode of fastening is indicated in fig1 . in that case , a clamping ring 19 tightenable through the use of a screw 18 is placed around the outer periphery of the connecting flange 16 of the washing similarly constructed connecting flange 20 of the washing solution container 17 . the clamping ring 19 has obliquely extending sides 21 , so that upon tightening of the clamping ring 19 , the two connecting flanges 16 and 20 are axially pressed against one another by the sides 21 . in the case of the embodiment illustrated in fig1 the ring part 1 is constructed overall in such a way that with a front - loading washing machine it takes over the function of a front end wall of the washing solution container 17 . for this reason , a sealing element 22 is inserted between the two connecting flanges 16 and 20 . upon tightening of the clamping ring 19 , the connecting flanges 16 and 20 are pressed against this sealing element 22 , so that the washing solution container 17 is sufficiently sealed at its end surface . furthermore , a wall part 24 extending radially into a space 23 bounded by the inner u - limb 3 , is formed on at the u - shaped ring part 1 . this wall part 24 has a middle region formed as a loading - in opening 25 . an obliquely rising flange 26 extends out from the edge of this opening 25 . a sealing sleeve 27 , which is fastened to the flange 26 in a known manner , produces a connection to a loading - in opening 29 provided at a housing 28 of the washing machine . in this variant embodiment , the u - shaped ring part 1 is at the location of an otherwise required end wall of the washing solution container 17 . the end wall of the washing solution container 17 and the balancing weight are therefore integrally connected together .