The plug snaps into the compressed-air connector and prevents dirt from entering the connection. My compressor is portable, so I pull-off the hose and plug in the tiny plug to take the compressor along.

Please rotate .stl file 180° in your splicer. 

I added a drawing from this plug, so that you can adapt it to your needs.
Model and Drawing is made with OnShape. OnShape is realy easy to use, very intuitive.

I printed it in PETG, should work with PLA too.