1967 barracuda locking gas cap insert

Some advice: DO NOT use the anti-siphon spring. It is a huge PITA. It interferes with the flow of modern gas pumps so that you can only trickle in fuel manually at the slowest setting -- you can't use the stops. Nothing like standing there bent over squeezing that handle for 20 minutes while your fingers go numb... My Barracuda FB had one of those in it and I eventually pulled the tank and replaced the filler neck just to get rid of the stupid thing.