An exhalation valve to match my filter. in fact, the threads are the same so if you navigate to my filter holder design ( https://www.thingiverse.com/thing:4513562 ) you can select any of those covers OR use the files provided to make/edit your own.
The valve flapper bust be heat bonded to the valve body, a soldering iron on 300f is best suited for this task. PLA works great. to put these on a mask, cut a hole to BARELY fit the screw threads, and screw them together. it was designed to screw together over anything thinner than 4mm. Please tip! We've had a rough time due to Covid-19.

Creality

Ender 3

No

No

1.8

10%

increase wall thickness to 2mm or more for a durable part.