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