These high-quality pneumatic push-fit couplings have a 1/8" thread and screw directly to the bowden heat sink or any printed parts you may have that need to be converted to take PTFE tubing.
They are drilled out so that the PTFE tubing will run all the way through the fitting and into the part that you are screwing it into.
Inner v Outer Diameter illustration
For 4mm 1/8" OD Tubing (1.75mm filament):
Nominal Thread Size: 1/8" BSPP
Thread Length: 4mm
For 6.3mm 1/4" OD Tubing (3mm filament):
Nominal Thread Size: 1/8" BSPT
Thread Length: 8mm
Overall Height: 28mm