I was having a bit of a time keeping my M6 PTFE fittings square when trying to thread them in to a few 3d printed parts I had made so I came up with this simple driver. 

My driver is printed on quick draft settings with whatever the default in-fill is, it required nothing special to work. 

I don't think it really matters what you print it out of as you're screwing brass in to 3d printed plastic, just be careful you don't tighten it too tight as your 3d printed part may fail. 

This MAY work with other fittings as well? I printed it for the fittings I had on hand.