A lazy person con designed to do a 1/2 decient job of cleaning the underside of the deck which in most cases is a fools errand and promote the premature failure of spindle bearings unless you follow a rigrious proceedure which generally makes more mess and takes more time than shoving a gloved hand under there and pulling the thick lumps of grass out while it is fresh & soft which in most cases is actually not needed and makes no difference because the grass will have built back up after 10 minutes of mowing the next time you use it .