must be manufactured of rigid material and the wall member 14 of flexible material or the wall member 12 of flexible and the wall member 14 of rigid material it can also be seen in these embodiments that the groove with reference to the direction of movement of the wall member 14 and the tongue element forms projecting edges 214 creating an undercut on the other hand a rigid inseparable joint construction between both wall members to be joined to each other can be achieved with the joint 2 of the invention to this end it is merely necessary that the profile groove 21 which receives the tongue element 22 be quite in constrast to the groove shown in fig2 which ends before reaching the outside and may thus be termed to be 34 closed 34 provided as a through groove extending to the outer surface so that the tongue element 22 can be pushed into the wall members which come together by butt joint the tongue element 22 will only show little or no elasticity in such cases so that the wall member 14 cannot be extracted in direction a from the wall member 12 resp the unit determined by this wall member in order to prevent a slipping out of the positioned tongue element in such cases it is of course possible and in many cases advisable to provide some type of locking elements known to the man skilled in the art which enable a locking of the wall members in the desired position while four tubular joint struts 301 are used in the casing cell of fig1 and 8 for the manufacture of a rigid structured unit of upper and lower wall members the struts being mounted fixedly by upsetting riveting or other.