This is an adapter for E3D V6 hotend clones for Bowden extruders to be used in Direct Drive applications. It centers and supports 4mm PTFE tube from extruder to heatsink's 4mm tube hole.
Felt lazy rolling my own, found bratan's insert and printed. The threads didn't match, the rest is history. Bratan's insert has a 1.5mm pitch, too coarse for the V6 clone I have.
Figured the pneumatic fitting insert the hot end came with should have a pipe thread (OD was 9.35mm), used G 1/8-28 (G9.728X0.907) thread. It appears to match the V6 clone's thread.
OAL is 9.5mm. Threaded section is 7.5 mm long. Center hole is 4.3mm.
Pic shows one (white) insert next to the pneumatic fitting and another (black) already installed in the heatsink.
Enjoy ;)