That's the deal, only a key lock. No cap. The thumb latch was discountinued about 76 or 77. Seems an accident where a guys helmet hit the thumblatch and opened the cap caused the recall. If you have the thumblatch, don't do the recall. Through the 80s, the recall was almost manditory, so only a few thumblatches still exist, making it rare. My 350F has the recall, but I have another tank with the thumblatch!!!
