If this helps.
something doesnāt add up. Look at my screen shot. I have the diameter of the flange at 75mm as shown in your sketch. It looks to me as if the edge of the hole is roughly on the edge of the flange but when I place the hole at 38mm, it clearly overlaps the edge of the flange.
Is the diameter of the flange really 70mm instead of 75mm?
Hereās a little gif to help you on your way.
So itās OK if the screw holes overlap the flange as in my screen shot? They donāt do that in the photograph. At least not by as much.
Thanks Box, you guys have so much knowledge, it beggars belief 
This is something I can āadjustā with the final 3D print, if needed making the holes elongated.
OK. Give me a few minutes.
If you completed a introduction to sketchup tutorial you could draw this pretty easy.
Thanks will have a look at that, trouble is too much to do or learn and not enough years left.
It wouldnāt take long mate, never wanna stop learning!
many thanks Dave, I will download that and be off to the man cave to see what I can come up with.
Also thanks to all of you for making my first visit to the forum such a pleasant and very helpful and informative one.
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Agreed and not wanting to sound melodramatic, I am battling a terminal debilitating disease which means Iām tethered to an O2 supply 24/7 and Iām not going to let it prevent me from enjoying all the available toys etc that are out there. Thatās why a lot of the time I do the āman thingā and jump straight in hoping I stumble across the answer. But what you say is right.
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Cool! Thanks for sharing the picture.