One pair (2) of grub screws for all sizes of HyperSpinner.
This is the tiny hex end screw that fixes the spinner to the gearbox output shaft. In our opinion only one screw is required, to give one point and one surface clamping action. Two grub screws result in two point clamps, which may be less effective.
We recommend filing or cutting a flat in the gearbox shaft for the grub screw to engage in. This eliminates the possibility of the prop flying off forwards if it becomes a little loose, and keys the spinner to the prop shaft, to ensure it does not slip in rotation.