1-3/4" x 6" Diesel Fuel Filler Neck with Green Cap | Mill Supply, Inc.
Boat Gas Cap, 1-1/2inch Boat Marine Deck Fuel/Diesel/Water Filler Cap, 316 Stainless Steel Water Tank Deck Fill Filler with Keyless Cap Used for Boats, Marines, Yachts, Caravans - Walmart.com