This is an NOS assembly line original vented gas cap, Ford part # BOA 9030-A.  It was used on 1956 and early production 1957 Thunderbirds. The cadmium plating is show quality. Perfect for replacing a missing or aftermarket gas cap with an assembly line original.   See my eBay Store for more Ford and Thunderbird parts. We charge actual shipping, are glad to combine shipping or your welcome to pick up the part at our shop. Thanks!