4 simple joining cylinders for PTFE tube. Two of the cylinders are friction push (for white and Capricorn tubes) and the other two use the large or small push connectors. 

The sides are segmented to help with grabbing and twisting. The larger push connector tube has an arrow for direction of flow to limit the sticking of the filament when initially pushed in. 

They seem simple projects but I found the screw threads needed a bit of playing around to make right. I think they print well with thick walls (5 layers) and 70% infill.