Antique Victorian Ostby & Barton 10k Gold & Ruby Belcher Mounted Ring Wedding Bands I have looked but could

I have looked but could find nothing on this mark

the number 375 for 9kt gold and a lower case h which is the date letter for the year 2007

F color and Vs1 clarity

8mm in diameter and the surrounding opals measure between 4mm - 2

The piece is hallmarked 18K but there is no makers mark

Antique Victorian Ostby & Barton 10k Gold & Ruby Belcher Mounted Ring Wedding Bands I have looked but couldAntique Victorian Ostby & Barton 10k Gold & Ruby Belcher Mounted Ring. The ring is in excellent estate condition and ready to wear. It is signed OB 10K. It is set with an approximately 1 carat synthetic ruby. The ring is a size 5. 5 5. 75 and weighs a total 2. 3 grams. The ring stands 10mm high off of the finger