Hi Fivetide
That hole is way too big for a 10mm insert, have a look @ this
https://www.tappex.co.uk/products/br...msert#selector
Not tried to find a 10mm one but you can get an idea of the wall thickness. If you have a lathe you could make your own, i did so for my window project, Tappex sent me 12 samples and i just copied them(they seemed expensive @ the time and i needed 48)
Obviously you would have been better finding your insert before drilling the hole.
Regards
Mike