On a semi-mount hub, cushion, oval, and round describe the center-seat shape, not a finished diamond ring. Compare the outline you want, then confirm CU / OV / RD millimeters and metal on each listing.
Finished cushion, oval, or round engagement rings with a center stone included are a different product type. Use these hubs for settings / semi-mounts / without center stone as labeled.
Browse sibling shape hubs on this site, then use Design Lab if no listing matches: https://www.syzjewelry.com/pages/designlab-custom-jewelry