A device for applying a medium in the form of a liquid or a paste to a moving substrate, the substrate being a surface of a web of paper, a paper board, fibrous material and/or a transfer element including an application chamber, a first element, a second element and at least one limiting element. The first element is associated with the application chamber on an output side of the application chamber in a direction of movement of the moving substrate. The second element is associated with an input side of the application chamber. The at least one limiting element is associated with a lateral end of the application chamber. The at least one limiting element adjusting a width of application of the medium on the moving substrate. The at least one limiting element having a flexible sealing plate that substantially seals a space between the moving substrate, the first element and the second element. The sealing plate includes a fitted wearing body that is directed toward the moving substrate, with the wearing body being proximate to the first element and the second element.