Quick COVID-19 related post, a few weeks ago when this was all kicking off I managed to get a nice deal on a set of five Sundström P3 filters and 25 pre-filters. The only issue being that they use a proprietary thread designed only for Sundström masks. I have a Yugoslavian M1 gas mask which takes 60mm thread, seeing as though modern filters use the 40mm NATO thread I picked one of those 40-60mm adapters up for a few quid on eBay the same time as I was getting the filters.
Sundström and arco do sell adapters to these threads but now that we're all in the shit they've decided to pull stock from civillian hands and re-direct it into the services.
So to not waste £20 on filters I 3d-modelled my own adapter. The model is composed of two parts, the thread and a bit that sits on top of the filter.
Firstly, print the two pieces, I used an Ender3 3d-printer with 1.75mm PLA grey filament.
You can see where this is going... thread goes in hole and circles latch on, I added a bunch of hot glue to keep the whole thing air-tight on the thread.
The bottom part is measured to be a perfect-ish seal around the rubber ring on the inside of the filter. I lacquerd the rim of the filter in hot glue and quickly pushed on the adapter to create a seal.
And tada...!, hopefully this helps someone out in the same situation :) I'm working on the pre-filter part since you can't exactly glue that bit on, I'll update this post when it's done.