Seeing as how this is a request to change a coin's page, and there is no possible field to add that information in, it is an impossible task, so I must reject this request.
With that being said, please re-post this topic in this forum as a 'Suggestion for Numista':
https://en.numista.com/forum/forum15.html.
A more comprehensive way for measurements would certainly be helpful (especially for oddly-shaped coins). And seeing how the Metal field was changed to be more comprehensive, I would imagine this is definitely possible to implement. However, this thread must first be posted in the correct section so it can be properly tracked.
EDIT:
Oh, but until a feature like this is implemented, you can always write the hole's measurements in the comments section. That... may suffice.