Making a strap buckle, question about the drilling size.

Hi guys ! Im a happy guy with my speedmaster 3861 but i'm also a maker. I just like to make stuff. And i want to make a leather nato strap (I have some interesting idea). I can buy any buckle from amazon or alibaba but i'm currently designing one in fusion360. I have a small CNC in my basement and some experience in machining (especially titanium).
I would like to know if someone here have experience in watchmaking.. Im looking for dimension and drill size. I found this picture:


So from that, I need to drill slightly bigger hole than 0.8mm, but i would like to know if, in the watchmaking world, you have some basic "rules" to follow. Standard values. If you are using "per default" a 0.9mm drill for the spring bar hole for example or a 0.8mm because any spring bar are in reality a little bit under 0.8mm to fit a 0.8 hole.

Thanks a lot. If you are interested to see the project, let me know, it will be a pleasure to show you. Im really new in this world but have some experience in machining, design and (a lot) of gunsmithing in my past. And sorry if my english is not perfect.

Never see this chart before. Thanks a lot. Printed and on my wall with my other charts.

Im wondering if somebody can help me choosing a good spring bar ? Can I trust amazon or they are really bad ? Thanks

Thanks guys I will make a new thread and post all the development of the project, drawing, picture, machining etc