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