anti-twist device is intended to be fixed. Then the anti-twist device has to be pushed down (fig. 3), until it covers the hexagonal or square profile and the lateral brackets of the anti-twist device engage [...] the position of the plug it is possible that the anti-twist device cannot be pushed down directly until it engages in the lower latching groove, because the anti-twist de- vice butts on the hexago- nal [...] to the left or the right (fig. 6), so that it can be pushed over the hexagonal or square profile, until the lateral brackets of the anti-twist device engage in the lower latching groove of the plug (fig