I took my single handle Delta faucet aerator out, soaked it in vinegar for a day and put it back. Somewhat better. but still some crud on the screen. So I bought a brand spankin' new 15/16 male threaded aerator - which looks identical to the original. I can't get either one back in at all. This is really blowing my mind. Came out easily and the first on after I cleaned it went in fine.