Oil tank cap key -- for gas & oil tanks where the cap requires one of those six shapes to unscrew. A couple of different styles have been shown in the MVWC Newsletter over the years. Check design patent numbers D 160,645 & D 160,646 (Oct. 24, 1950) in DATAMP, or pg. 2 of the Sept. 2010 MVWC Newsletter. D160,646 matches your "starfish."