So these things work great but they stupidly do not fit into any curtain rail. I foolishly determined only at the hanging that depending on the window I probably another curtain rail. If the opening of the clip was too narrow and the rail system itself is too low as these clips would fit in. If you try it somehow still get shut purely do not let them move naturally. So best anguggen earlier times your tracks if there is even enough room for these things. You need 8mm in width and height.