Abstract: A mounting disk arrangement is provided for the fixation of loosely installed sealing sheets of a synthetic resin, wherein the mounting disk is attachable to a substrate, such as a substrate on a roof, for example a trapezoidal roof, by means of a screw passed through the mounting disk. In order to prevent unturning of the screw, a blocking mechanism in the form of a member attached to the mounting disk and engageable in the screw slots of the screw is provided. In preferred embodiments, the blocking apparatus consists of a leaf spring, while other embodiments include plate members attached to the mounting disk.