This is a little stabiliser pin for the XS Fan Duct Plate from Dev-In Labs (https://www.printables.com/model/251191-ender3-adapter-for-e3d-revo-hemera-originalxs-v2) which can be used to mount Hangtight's fan duct (https://www.thingiverse.com/thing:4042492) to the Hemera XS.
As the upper slot cannot be used due to interference with the fan, you can mount this plate with only one screw. The pin should be pressed into the upper T-nut-slot of the Hemera motor and sit in there tightly to prevent movement sideways, while still allowing the fan duct plate to move up and down.
Printed with a 0.25mm Revo nozzle at 0.1mm layer height.
The author hasn't provided the model origin yet.