What is the point of trousers’ second button?

[BigBrother]

I’ve seen this all over with my vintage trousers (40s-50s) and I’ve no clue what the point is.

There’ll be the standard button at the top of the fly and then a zipper, but between A and B there’ll be a second button, usually mated with a small flap, and virtually always further into the left side than the primary button.

I’ve tried wearing them both with and without this button done and, for the life of me, I can’t detect a difference or what the purpose of it is, and yet there must’ve been one.

Help?

Thanks!

 

[Peacoat]

Maybe for strength so all of the stress isn't on one button.