These are modular SMD feeders for manual SMD pick & place. STLs are exported in standard sizes: 8mm, 12mm and 16mm. If you need different size, please use customizer to create your onw design.
You can print them in different colors and combine as you need (eg. black for resistors, orange for capacitors etc.)
Print two rails https://www.thingiverse.com/thing:2414978, fasten with screws and slide feeders into rails.