This is an end cap for the Trim+Go Levolor shades to protect the sharp edge of the material. It also helps keep the tube inside the loop without sliding out, if you do not use the Levolor grip piece.

These are designed to be friction-fit, and a gap can be left between the inner tube and the printed part in order to not compress the vinyl material. They should be set to where the vinyl is under the lip of the printed part, and not wrinkled.

I've attached the fusion model as well.