Filter W/Out Biohazard symbol

The thread on GasMaskFilter_Top.stl is designed according to the NATO spec STANAG 4155. It's commonly referred to as "40mm NATO thread".
For basic assembly, you'll need the following:
Some form of filter medium
1", #6-32 machine screws (x6)
6-32 machine nuts (x6)
Disclaimer:
This is not intended to replace proper respiratory protection. Try this at your own risk.
Thank you uumeran and Eric P.!