This is version two of a Bowden tube clamp using a nut to compress the fittings instead of a zip tie.
I used part of a designby krtektm who also created a compression type fitting.
It should fit the standard 4mm ptfe tube and clamp over the collar of the fitting. You will have to clear out the slot that fits the collar as there will be some filament in the groove that should not be.
Here is the fitting I based my idea on.
May I also recomend this design that I just found,its a neater job I think