We have 3 size Small left of the Avon FM12 Respirator Gas Masks. All 3 are missing the threaded cap that goes over one of the 2 ports. These are available online at times or you can simply install 2 gas mask filters. The cap feature I believe is so you can wear the filter on either side. It wont affect the performance of the mask that I can see or you can complete On your own. Its a standard 40 mm NATO size threaded fitting. Also any 40mm filter will fit the port. Each unit is complete with a drinking tube built in as well. The head harness of the FM12 consists of elastic strips, ...