[marklbucla]

I looked but didn't find a direct answer.

I'm guessing I already know the answer, but the basic difference between them is that the Express has the grooves on the inside of the cap and smooth lips while the Wingmaster/Police has grooves on the outside to mate with the ball on the barrel ring?

I ordered one for the Police/Wingmaster but I think I was sent one for the Express.

[Eightball]

Near as I can tell, you're correct.