USA Industrials - O-Ring: 43 mm OD, 37 mm ID, 3 mm Thick, Fluoroelastomer - 47418538 - MSC Industrial Supply
Express Water Whole House O-Ring Replacement Kit 5.5 in. O.D. Dia O-Rings for Filter Housings 3-O-Rings with Lubricant Tube PRTORINGWH3 - The Home Depot