This knobs is used on the overhead, on the Pressurization Altitude selection panel to set the cruise flight altitude.

You will find recess holes, these are a guide to where the grub screws need to be, you will need to drill these out further. I have also not placed a centre hole on the bottom of the knob, due to some people needing D shaped holes and others circle.
The grub screws are at a 45 degree angle to the center