gas cap help

[blue74chevy]

I am looking for a stant locking gas cap for my 1974 K20, I am looking for the kind that looks like the one in this link

http://shop.oreillyauto.com/ProductD...pe=112&PTSet=A

but when I got one that said it fit my truck it did not fit, it would go in and lock but it would be loose and would wable
I found an older stant at a swapmeet and it did the same thing, anyone one no the part number that will work? my truck was made in california, I know that make a difference som times