In order to improve an insert for an opening in a wall area of an appliance comprising a housing socket, an assembly device provided on the housing socket, with an assembly section which can be guided through the opening in the wall area and has snap elements which engage behind an edge of the opening as well as with a pressure ring which is arranged on the housing socket at a distance from the snap elements and can be adjusted in the direction of the snap elements by means of an advancing guide as a result of a rotary movement about the central axis, in such a manner that a secure assembly of the housing socket is possible, it is suggested that the pressure ring be rotatable in a first direction of rotation in order to secure the housing socket and that the housing socket be adapted to be fixed against any co-rotation in the first direction of rotation by means of a holding section element.