Hi Basihs,

Here's a ring blank based roughly on the photo you supplied.

First I created a circle at 9mm Radius for the finger size.
I then created the ring Profile then used Rail Revolve as Michael has already suggested.
I then switched to the Right View & created two arcs then Joined them to form a closed shape.
While still in the Right View this new closed shape was Mirrored to the opposite side of the ring.
Still in Right View select the ring, click Boolean Merge & select the two closed shapes.
Delete the two sections that have now been cut from the ring.
Select the inside circle(finger size) & Extrude it with "both sides" checked.
Select the ring, click Boolean Difference & select the Extruded inner shape.
Select the ring again & click on all the outer edges of the band on both sides.
Click Fillet & enter 0.7mm.

That's it, but you'll still need to create the settings for the Diamonds & the centre stone.

Hope this helps, Colin