13L602 up for sale is a military onan generator p/n 159-1137 or 84-13050 fuel or tank cap covered under NSN 5342-01-305-3401 , this is around 4 1/2 dia and have the valve to close it for fording non venting,comes with chain and retainer band also,note : some of our stock is olive drab green color and some are painted black as shown in the photos you might get green or black or let us know your preference we can try to send you green or black depending on how many we have of each in stock , buyer to pay calculated shipping and packing to your locations , see our store for more items like this, thank you RWK .