Boat Deck Fill/Filler Cap Keyless - Angled Neck 1 1/2"- Fuel Gas Marine 316 Stainless Steel Convenient, keyless design - lift built-in tab on cap and turn to open or close.ose. Precision cast 316 marine grade stainless steel. Maximum corrosion resistance and durability in the saltwater environment. Polished to a beautiful, mirror-like finish. See additional details and measurements in product description below.