This is a pneumatic fitting for 3mm tubing (e.g. 2mm inner - 3mm outer diameter for 1,75mm filament), with an M5 thread and a very good resistance to retain the tubing.
The exact reference is MA-12-03-M5 (see the MA series for the datasheet http://www.socafluid.fr/Produits/Raccords_Pneumatiques_Sopra.html)

I'm ordering them in bulk for my FoldaRap, and offer here some spares.

They are compatible with the emaker/repprappro hotend (same M5 thread), but a little bigger than the original Camozzi fitting, maybe also compared to the new brass fitting, so the mounting-nozzle.stl printed part will need an eventual filling or adaptation to fit (you can see an adapted printed part at the end of this post from richgain, he also had to cut in the stripe of ptfe to make for the larger body)