The American Plumber OR-233 O-ring is 3" in diameter and fits Housing Models WLCS-1000, US-600, US-640, SY-2000, SY-2300, SY-2300S, SY-2500, SY-2650, RO-3000, RO-3500, WRO-3000, WRO-3500 and Ace 4158622 Water Filter Housings. American Plumber part 151231-51.