This specific 3D model, "Engagement Ring 3D print model 12", is an asset made available by "Unknown author".
Can be downloaded at "Unknown platform" by following the link.
Usage of this 3d asset is subject to the "Unknown license" agreement.
STL (Stereolithography, filesize: 9.42 MB), 3DM (Rhinoceros 3D, filesize: 3.19 MB)