3M Style Respirator Filter Bayonet Style Male Mount
This is my replication of the connector on a 3M 6000DD series Half Facepiece Reusable Respirator. Requires 35mm OD 21mm ID foam ring for propper seal with cartridges. It serves no purpose on its own but can be added to whatever filtering hardware you might be tinkering with. I do not advise that you depend on this for any critical safety application.