This flush fitting cap is slotted for opening with a (separate) slot style or 2-prong key.
It features an O-ring seal, and a braded stainless steel keeper chain.
This umarked cap fits the following Attwood deck fills, only:
• 66406 - Fill body marked Gasoline
• 66407 - Fill body marked Diesel
• 66408 - Fill body marked Water
• 66408C1 - Fill body marked Water, in blue