MosMax Electronics battery holders are made of solid nylon and injection molded (no 3D printing).
They are available for 18650 and 20700/21700 cells (with 21700 they protrude a bit).
The included keystone contacts can be used for series or parallel connection. They can be soldered before installation or when inserted. If used, please ensure that the nylon holder is not overloaded or too hot when soldering.
Flux soldering aid can be removed with acetone or alcohol without damaging the holder.