Idle Mixture Screw

[bigfour]

So, I've turned my carb so I can see underneath it and I'm looking for a brass plug but I see two brass things...

The lowermost one looks like a flathead brass screw kind of inset in the carb.

The other one is a slightly larger brass cap with a small circular indent in the middle of the cap.

Which one is the idle mixture screw/cap? I'm thinking the second one is the cap I need to remove but I just want to be sure so I don't drill through something that's actually important. Thanks.