A connection element of the present invention has several jaw sidewalls that are oriented in different directions, whereby two jaw sidewalls at a time can be braced against each other to receive a component part. At least one jaw sidewall can be set so that it is adjustable on the connection element and this jaw sidewall projects by a lateral leg into the inside of the connection element. There is in active connection with an adjustment element that is to be activated from the outside in a direction to brace or detach the jaw sidewall. With the connection element according to the invention, it is possible to connect the plates of a shelf construction system together without nails, screws and the like.