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