The adapter allows you to use an AA (LR6) battery instead of a C (LR14) battery.
It is 12mm tall: you can stack 4 of them and get the exact battery height, but if you want to save plastic you can also use only 2, or even a single one if you are in a hurry.
Compared to things 39478 and 4205:
Print in ABS, 0.33mm layer height.
Print lots of these and save $ and waste.
The author marked this model as their own original creation. Imported from Thingiverse.