They holds the bowden tube very well when using the Creality CRSE Micro Swiss hot end. I hope one day I can find a male ended compression fitting like these ones so the tube cannot loosen itself from the connection at the extruder end. One draw back is that if you have to change the tube - it is a complete tube change as one will never slide the fitting off. On for life - explaining the strong connection. I used the 3 that comes with the kit - suggest a few more as I could not find any 4 mm sleeves any where in town. Got 5 more from Spool3d on special order.