On assembling the two hotends I had inserted the Bowden clip and then "tried the ptfe tube for length" BEFORE cutting it to length (ooops) as initially the tube had not gone in for more than a about a cm. I thought that maybe the clip would have a centering effect. Unfortunately it appears that once the Bowden clip is in place the ptfe tube can't be removed? . I assume that this is the function of the Bowden clip? i.e. a sort of ratchet effect. As it is, the ptfe tube will not insert any further and can't be removed either. Unscrewing the Heatbreak shows that compared to the "good" assembly (without the Bowden clip inserted for now ) the ptfe tube isn't inserted far enough. As I can't either insert the tube further OR remove it ( is there a procedure other than destructively cutting off flush and drilling out? ) then I may order some more parts. What would be good to avoid this is to see if the ptfe tube fits to a depth of about 33mm (half its length) WITHOUT the Bowden clip inserted. Assuming it does fit then fit the clip and insert again. Essentially the ptfe tube should butt up against the Heatbreak inside the heatsink. The ptfe supplied was cut at an angle whereas it would seem better to cut it absolutely straight before cutting it to length, this may also remove any distortion preventing it from inserting correctly. Had the ptfe tube been fully inserted then I would have just cut the external bit to length. ======================== With a little brute force and ignorance, by twisting the ptfe with more force than should be necessary, I have managed to get it further into the heatsink and it stops now against the Heatbreak. I will now cut the protruding bit to length based on the "good" one. Really simple check but I think it is worth adding to the instructions to check the ptfe tube will insert to about 33mm BEFORE fitting the clip.