This is a spacer for the extruder to improve filament path. The gears had to much play and caused many problems (especially with TPU). There are 3 spacers, you have to find out which one fits best for your gear set. The number in the file is the thickness of the spacer
For more details please check my previous model with all the pictures. Make sure that you also use the remix of the extruder level. I needed both files to get it to work
https://www.printables.com/model/231989-cm3d-and-vertex-extruder-lever-remix-aligned-with-
The author remixed this model.