Sea Dog Keyless Fills are made from Cast 316 Stainles steel with the cap molded from fiberglass filled nylon. Each deck fill has a specail cap with a built-in key for easy cap removal. The hinged key can be locked in the upright position to open or close the fill and then recessed into the cap for a flush surface. In addition the caps are molded in special colors to help prevent the dangerous and costly problems caused by placing fuel in water or waste tanks or vice versa. The cap threads are 1-1/4'' - 11-1/8''NPSM Straight, Gas, Diesel and water caps include attachemtn chains. Black caps will all marking are available through specail order.