Gems:D2.0mm - 2 pcs per ring
Volume = 494.5 mm3 for 20 mm size
Volume = 422.8 mm3 for 17mm size
Fresh original simple laconic design of wedding rings. The idea lies on top, but I have not seen such. Halves can be soldered, and can be worn in a puzzle fashion unsoldered.
On 3dm-file you can quickly create rings of the size you need without fitting the stones.