These spinner covers is designed to fill the gap between the RVJET fuse and the spinner that comes in the RVJET power package. The cover has cooling outlet ducts to let cooling air out from the ESC and motor compartment.
They are meant to be glued directly on the rear of the fuse. If needed there are some slots into which 3x1mm CF-strips can be used for reinforcements. An up-arrow shows how the cover should be aligned.
The cover is designed to be slightly smaller then the foam since foam can shrink depending on temperature and mechanical stress. In the renders you can see a slight edge but it should look better in real life. I have also not tried these from Shapeways myself but have printed using a FDM-printer.
NOTE: This cover fits if distance to spinner from motor mount is ~60mm.