The main diamond in my engagement ring was kicked out during a "no holds barred" Michael Jackson dance-off. Ridiculous, I know, but I was lucky enough to find my diamond and would like to set in a pave mounting with space for a 6mm center stone. Would my 5/8 princess cut diamond fit?
Probably not. A 6mm princess cut mounting would require a princess cut diamond just over 1 carat ( approx 1.25 carat) Your diamond at 5/8 is half that weight ( appx .62 ct)
Your stone would need a mounting size a bit smaller than 5mm, unless your diamond is cut very shallow, which might be able to fit if your goldsmith can cut down the setting to fit.