Reverse bowden adaptor

It's a pretty simple model, it covers a threaded bowden coupler and has a 4mm mating hole each end with the top hole tapered to 2mm to make filament changes easier and provide alignment for a smaller inner diameter length of Capricorn or similar PTFE that goes into the hotend. 
 

This was designed for a Biqu H2, but it's pretty low profile so should work with any extruder that uses a threaded bowden coupler. Changing filament is a simple case of push and pull, though the actual piece is design to be easily slid up if you need to manually feed the filament from one tube to the other, so far it's making things a lot quicker

Why do this?

A reverse bowden tube should have a wider inner diameter (3mm) than a standard tube, but once you get to the hotend you have play which means the filament might not insert cleanly, making filament changes annoying and slow. You add a short length of tight bowden tube to the coupler and then slide the adaptor over, the inner taper helps the filament transition from one tube to the other and even if it doesn't, you just slide up the adaptor without having to unscrew the bowden coupler.

Print settings

Finer settings will probably work better, but this works just fine at 0.3 in PLA+, You cal print without support but you'll need to do a little post processing to remove the wispy bits inside. Sliced with superslicer, I couldn't successfully remove supports, but YMMV. You might need to adjust the model a little depending on the fairly tight tolerances, you want a firm grip on the tubes and a snug, but easily removable fit over the bowden coupler end, I've attached a step file anyway :)

Have fun!