This is a 20mm riser block for a JetBlack Turn Block. To fit the Prusa Mk3 build Plate it doesn't completely cover the base of the turn block but should be sufficient for stability.
I sliced it to minimise filament but to give enough strength, key slicer parameters for me were:
Above used 188gm/63m of 1.75 filament taking 6hr23min to print.
You can if needed adjust the height in slicer if you have a different trainer.
The author marked this model as their own original creation.