the fastening device 2 not shown after the latching plate 8 has passed beyond the tip of the resilient latch 3 the spring action of the resilient latch 3 is relieved again and the latching plate 8 is fastened behind the resilient latch 3 as the resilient latches have opened up thus the latching plate 8 can no longer be pulled over the resilient latch 3 see in that respect fig4 a and 4 b for again releasing the latching plate 8 the resilient latch 3 has a second portion 22 of the inclined surface 20 which rises from the notional spring axis a towards the free end 6 of the resilient latch 3 that portion 22 serves as an inclined disengagement portion when now the rear wall 111 is pivoted in the direction of the side wall 112 and thus towards the resilient latch 3 the resilient latch 3 is again compressed by the latching plate 8 and the rear wall 111 can be removed from the side wall 112 or the connecting fitting 1 again that dismantling process is shown in fig6 a 6 b and 6 c in which the wall part 103 already has an angle differing from a right angle relative to the wall part 104 the latching plate 8 compresses the fastening device 2 u2014 or its resilient latches 3 and 4 again thereby permitting removal of the wall part 103 that is made possible by the second portion 22 see fig3 b and 5 of the inclined surface 20 which rises from the notional spring axis a see fig2 b and 5 towards the free end is inclined.