This is a pneumatic quick disconnect fitting with hose barb. It is customizable for three different sized hoses. I made this so I could easily hook up my print of http://www.thingiverse.com/thing:25624 to my air compressor hose, which has a quick-disconnect fitting on it. Warning: I have no idea what a safe operating pressure is for these things. I only run 30-40 psi to run the steam engine. I would not take them up over 50 psi. This thing is printed in two parts. The barb part is printed with a larger diameter base so that it sticks to the build plate. Cut this off with a hacksaw, then glue it inside the other part. This thing comes in three different hose sizes; you can either print one of the supplied STL's, pick one in the customizer, generate all three via the customizer, or get the .scad file and modify it to your heart's content.