This knob is used on the Airbus Weather Panel, the other knob is also uploaded on my profile

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 90 degree angle to the center