4 inch Pop Up Center Drive, Polyolefin Pop Up Drainage Emitter With UV Inhibitor, It Fits 3 inch and 4 inch Hub Sewer and Drain Fittings, Pop Up Does Not Rise High Enough To Interfere With The Mower, and It Blends Into The Surrounding Landscape, Since The Emitter Is Closed During Dry Weather It Keeps Out Debris and Rodents.