Single 18650 Battery Holder

Here's a basic 18650 battery holder.
It uses the commonly available contacts that can be purchased on E-Bay, Amazon, and the like.

Update Jun-23-2019: I just uploaded a series of new stl files.
The big change is that both battery contacts simply sit in a recess rather than the negative one sliding into a slot. A small dab of glue behind the contact holds it in place nicely.
The other change is that I've built the same design with six battery lengths: 65mm-70mm to hopefully accommodate protected cells that are a bit longer.