Was missing on vacuum cleaner for years. Didn't know it existed. Didn't understand why different height settings seemed to make no difference. Didn't know why the roller brush thing - I forget what it is called, a beater bar? - kept breaking or wearing out, and wondered why some parts of the carpets were worn awfully thin. Somehow figured out that this piece was missing. Easy to install if the base plate is not broken. Ours was, so this was easy to replace once the base plate got replaced, a less easy job. Just snap it in, being careful not to break the plastic on the base plate. The vacuum is a kenmore progressive and it works so well in spite of its age that I am glad to keep it going with periodic parts replacement.