FiftyFifty Wide Mouth Water Bottle Cap/Lid Replacement Cap for Fifty/Fifty Wide Mouth Doublewall Vacuum Insulated Stainless Steel Bottles. Cap will fit only Fifty/Fifty Wide Mouth Doublewall Vacuum Insulated Stainless Steel bottles. Cap Fits: 18oz, 40oz, 64oz Wide Mouth Doublewall Vacuum Insulated Stainless Steel Bottles.