J-RH5 is a retrofit model for large floor drains. Fits over a catch basin that is 5? or larger. Not for use with sub-floor depressurization. A flexible rubber flange attaches to the hard-plastic portion of the seal. Hold the Dranjer under the existing strainer plate. Push the strainer plate with the Dranjer back into the drain opening. Friction among the sides of the cover plate, the Dranjer, and the ring in the floor holds the Dranjer under the cover plate. Trim off the rubber that extends past the ring. You have retrofitted the Dranjer in existing construction. The J-RH5 cover plate is 5? diameter. Not for use with sub-floor depressurization.