This sleeve is meant to be used to help folks with the sealing of the circulation pump that Kristian talks about in his excellent DIY video:
You would just slide this into the opened pump before spraying the electronics sealant to keep the spray off the other windings/magnets. Remove after everything is sprayed and you reassemble the pump.
The original Fusion CAD file is also enclosed if you want to remix.
The author marked this model as their own original creation.