Another Gas Cap Question

[DT1]

So I just received a non locking gas cap from Rock Auto. It's suppose to be for a 72 C10 with EEC. The problem is it goes on so loosely it won't seal at all. As a matter of fact, I'm afraid that if I hit a bump It'll fall off. So, I figured since it's a nice new chrome one, I'd just put it on my 71 C10. It fits the same as the 72. Way too loose! Rock auto gives plenty of choices as to what cap to choose from. Obviously, I choose wrong. So, this cap was called a deep cam type with EEC. They also offer what they call a "Standard cap". My question is, does anyone know what the difference is between a "Deep cam" type and a "Standard" type?
Or maybe I should just ask what type do you guys use on your 72 C10's?
Thanks!