Depending on the size, equipped with 2 to 5 grooves for the accommodation of circuit boards or mounting plates. The top and bottom surfaces have recessed areas for the installation of membrane keypads. The side surfaces are flat, allowing for the placement of USB interfaces, D-SUB sockets, or similar on the sides. The end caps have a recess of 1.5 mm for the accommodation of foils. On the inside, there are domes (except for EL 620) for mounting circuit boards parallel to the keypad surface, which are designed in height to accommodate short-stroke switches.