A locking piece includes a housing which has a, in particular, rectangular housing opening and a slide which is arranged in the housing. At the housing side, the slide is guided so as to be able to be linearly displaced between two end positions and which has a locking arm which extends at right-angles with respect to the displacement direction of the slide and protrudes forward through the housing opening. A spring clip is arranged behind the slide, which spring clip extends in the displacement direction and which is anchored at the two clip ends thereof in the housing. The slide is arranged between the housing and the spring clip and is retained in abutment with the housing by the spring clip.