Finding out ring finger measurement for friend's surprise proposal.

[goldordust]

I was wondering if anyone could help with any suggestions of secretly obtaining a ring size without the person knowing.

My friend's partner tends to wear a middle ring finger on her left hand. I'm hoping he can either get this ring to me or the least get the diameter of the inside ring to work out the size of that finger on the chance she takes it off. I'm very aware the middle and ring fingers are different in size but by roughly how much? I'm putting a guess at about 2 sizes smaller hopefully this should be near enough to do only minor adjustments later as I am hoping to pave set on the shoulders on the shank.

Many thanks in advance for any insight or advice

[josef1]

Make it bigger then you can size it down but they will be able to fit it on there finger when it's presented