Mechanism for fastening casing into wall opening

A fastening mechanism for fastening a casing into an opening in a wall, the mechanism comprising:

• a collar element attached to the casing and arranged to be in contact with a first side of the wall, in a vicinity of an edge of the opening;
• a pressing element arranged to be in contact with a second side of the wall, in the vicinity of the edge of the opening;
• the collar element and the pressing element being arranged to co-operate to direct a pressing force to the wall in order to achieve a force that keeps the casing in place;
• and a screw means comprising a threaded part and an end part for turning the screw means, the screw means being arranged to move the pressing element in the longitudinal direction of the casing when the screw means is being turned and to achieve at least some of the force by which the collar element and the pressing element are pressed against the wall, wherein the pressing element is arranged to rotate about an axis of rotation of the pressing element between a normal position and a mounting position, the axis of rotation of the pressing element being substantially parallel with the longitudinal direction of the casing whereby, when the pressing element is in the normal position of the pressing element, the pressing element is capable of coming into contact with the second side of the wall to achieve the force that keeps the casing in place, and, when the pressing element is in the mounting position of the pressing element, the pressing element allows the casing to be pushed into a final mounting depth of the casing, and wherein the pressing element comprises a body and a beveled guide part projecting from the body and shaped such that when the casing is pushed into the opening in the wall, the beveled guide part co-operates with the wall to turn the pressing element from the normal position to the mounting position.