Abstract: A cap assembly for closing the inlet of a fuel tank comprising a closure cap for releasable mounting on the tank inlet, an anchor chain secured at one end to the underside of the closure cap and carrying a spring retaining member at the lower end thereof for positioning in the tank. The closure cap has a two part inter-engaging construction comprising a lower cap portion and an upper cap portion. The lower cap portion is formed with generally T-shaped anchor chain retaining slots which are adapted for receiving and positively retaining the upper end of the anchor chain in assembled position without auxiliary fastening means. The upper cap portion is formed with a pair of depending tangs which are adapted for releasable engagement with the anchor chain retaining slots in the lower cap member for preventing disassembly and removal of the retained anchor chain.