Lettmann assembly kit for installing the new backrests on the guide groove. On current Lettmann seats, there is a mounting buckle behind the guide groove. Here you do not need the assembly kit. If you would like to mount the new Lettmann backrests on older seat shells, you will need the mounting kit. Of course you can build the attachment yourself with a 25mm Ladderlock buckle, webbing and rivets or screws. Without the mounting kit, the fixed backrests may fall out of the mounting groove during use or when getting in and out of the car. The vario backrest cannot be adjusted in height without a buckle.