This is a 4mm wide silver band with a 2mm wide 9ct rose gold sleeve.
The silver ring is flat on the outside and rounded on the inside to make it really comfortable to wear. A 2mm section of the silver is removed and a 9ct rose gold piece is soldered on. A thin line is engraved to clearly define the two different colours.
This ring can come in different widths, in any finger size and it can also be set with diamonds.