Summary

An AA cell adapter to C cell. Much like others.

Save money on batteries. Decent quality AA's are a fraction of the price of cheap C's. While they only have 35% the capacity and therefore life span, they have ~17% the price of C cells in my estimation when AAs are purchased in bulk.
In locations where battery changes are inconvenient, it's still worthwhile sticking with C's. But in cases where battery changes are quick and easy, this will save you around 50% of the cost of batteries.

Printable without supports, slotted to reduce filament use.