Whats NDI mean when its on the inside of a ring?

A quick Google search reveals two reasonable possibilities: An alloy code, in case somebody needs to resize it or No Diamonds Installed (for insurance purposes).

Or how about No Divorce Immediately?

Or maybe it’s none of those, just the jeweler’s initials. Do some research.

NDI is a Hallmark usually refers to who and where the ring was made or designed by. Sterling silver has copper in it for strength so yes, you could destroy the ring. but if you are talking about going swiming with it on, no you will not hurt the ring.,