Split shank engagement rings have bands that split open to wrap around the central diamonds. The divided band creates a thicker base for a large stone; the diamond should be a bit larger than the gap created by the split. Some designers utilize a small split and place the diamond on top of it instead of nestling the diamond inside it.
A split shank band provides more space for engravings or accent stones. Instead of one trail of tiny diamonds on both sides of the large diamond, this kind of ring allows for two. It is common for celebrities to line all of the surfaces of this kind of band with as many diamonds as possible. The diamond could have a halo of smaller diamonds or other colored stones surrounding it. These bands look especially nice with square or emerald-cut diamonds. The edges of the band line up perfectly with the straight sides of the stones.
This style is seen frequently in vintage rings. Sometimes the sides of the band twist upward like ropes to meet underneath an iridescent stone with large facets. If the four strands have been set with clear diamonds, a stone of a different color could be used on top. The ring would still be recognizable as an engagement ring as long as the stone is a light, watery color. Even a perfect, white pearl could be mounted on top to play up the kitschy, costumey feel of the ring.
A split shank does not have to contain a literal split. Some rings have bands that expand into flat V shapes on both sides of the diamonds. This makes the diamonds look bigger, since there is no demarcation between the curve of the diamond and where it meets the band. Flanker diamonds could be placed right on the flat areas around the diamond.
A ring with this kind of band looks elegant even if there are no additional details on it.