Hubcentric 12mm Spacer size nut size

[f0mo]

Hello, I've read a few of you buying and fitting hubcentric 12mm spacers however being in the UK - all of these suppliers are in the US.

I have a company that can make them however I'm not 100% on the sizes needed. Can anyone share inlcluding bolt sizes for the 12mm?

Or better.. a UK suplier.

Many thanks.