This is a sterling silver wedding ring with a central 9ct yellow gold detail.
The ring has a smooth inside that is slightly rounded for comfort. On the outside, the ring is profiled so it looks as if it is three separate bands. The overall width of the ring is 6mm and each "bump" is 2mm wide.
The ring starts off as a solid silver band and a section in the middle is removed. Then a yellow gold section is soldered in place and the ring polished.
You can have this design with a rose gold detail in the middle instead of a yellow gold band.