One of the first parts needed is an adapter from 3M's bayonet-style filter port to the standard 40mm NATO port. This is a pretty simple part, but involved a few iterations to get the dimensions for the bayonet port, in order to get a good fit. This also involved creating the rounded thread profile in OpenSCAD which was a challenge, and something I'll cover in the next project log.

This adapter works really well on the mask, but I would actually be cautious about using it will a full-size filter, especially the military C2 filters. The reason is I'm not sure I really trust the plastic bayonet port on the mask to take the weight and torque of a heavy filter, especially when moving. The real goal here is to use an adapter to attach breathing hoses to the mask, so the next part will be a tilted adapter, and one that is compatible with the 40mm GOST fittings used by Russian-style gas mask hoses.