I bought a few new nozzles expecting them to come with that little tube that comes out of the nozzle. They didn't come with them after all, so I tried to reuse the tube I originally had in the printer. Turns out my old tube is 4mm OD and 2mm ID, but the new nozzles have 2mm holes for the tube to go in. I use 1.75mm filament, so it seems like to be able to fit the filament through the tube would be impossible barring a tube with an 0.125mm wall.

My question is, can I put the tube outside of the nozzle? That is, not stuck in the hole for the nozzle. In theory, the tube would still direct the filament into the right place. It looks like that might be the point of these new nozzles, since it seems so unlikely that someone would be able to stick a filament tube in the nozzle.

If not, where can I find the tubes I need? I've looked in a few different places and I can't find it. Or are the nozzles useless, and should I return them? Thanks for the help.

  • 2
    $\begingroup$ Welcome to 3DPrinting.SE! What printer do you have? $\endgroup$ Commented Nov 26, 2018 at 19:35
  • $\begingroup$ Just a cheap copy of a MakerBot Replicator. It prints really well, though, and Im happy with it. Any suggestions? $\endgroup$ Commented Nov 26, 2018 at 19:52

3 Answers 3


To answer your question directly, the PTFE tube (or a separate thin walled PTFE tube for the bottom part of the heatbreak) generally always is outside the nozzle, so yes (unless you have an all-metal hotend, then there is no PTFE tube up to the nozzle). But as read from your question, your setup has the tube included inside the nozzle (this is described in more detail below). However, you can change the nozzle for one that does not have the PTFE tube go into the nozzle but rest against the nozzle provided you can find the correct sized nozzle/tread for it.

The nozzles your printer uses are non standard nozzles that are featured on a few printer designs. It is called an "MK10" nozzle, but there is no such thing as a standard "MK10" nozzle. Different designs of the "MK10" nozzle exist. Originally, the "MK nozzles" are the creation of Makerbot; an excellent post found in this thread (all credits for the MK history go to user "vermon") discuss the development over time of the "MK" nozzles. An answer based on this posting is found here.

The nozzle your printer has is slightly larger than normal nozzles. The CEO of ToyBuilder labs explains the difference between an "MK10" and an MK8 in this video. Take care of the thread size of such nozzles, the "MK10" uses M7 threads, while M6 is more common!

"MK10" vs. MK8 nozzle

As explained in this answer, the use of the PTFE tube inside the nozzle is questionable. The heating zone in effect is reduced to the tip of the nozzle. The heat transfer from heating element, to heater block to nozzle is only possible because of the enlarged design and the flange that give extra surface area for heat conduction to take place. It is not expected that such nozzles are able to print optimally at high speeds.


Let me clean up a little nomenclature

The PTFE tube is either a Bowden Style Setup delivering the filament from the extruder down through the cool-end and to the heatbreak or just a liner in the cool-end and heatbreak for direct drive. In both cases they are to prevent clogs. In most setups it is not pushed into the nozzle which is in the heater block (they exist, see below).

The liner/Bowden tube guides the filament through the heatsink and into the proper Hotend/Meltzone. In the better designs intended for higher temperature like ABS (see left half), it ends in the heatbreak. This also has the added benefit of having less chance to leak if the tube slips a little bit.

Simple setups (see right half) butt it against the nozzle and thus limit the temperature range. This kind of butted setup can lead to leakage if the tube slips up. In either case, it is no problem to reuse the PTFE tube when changing nozzles, it is even advisable in the case of a Bowden setup as it might change the length of the path.

The nozzle is usually screwed into the heater block from below, and for best use, one screws it against the heatbreak in a heated state - this is called hot-tightening.

2 comon types of hotend assembly in cut view

If you somehow end up destroying your PTFE Tube, you can get them under the keyword PTFE tube, Bowden tube or Pneumatic PTFE tube on the internet.

PTFE inside the nozzle?

Yes, these exist, OP has them, they look like this, and are not what has become the industry standard. Nozzle with PTFE liner

I can think of no good reason to put an PTFE Sleeve into the nozzle, but someone did it, and it sis a valid approach. However, I see several problems with it:

  • the PTFE tube degrades if pushed deep into the melt zone and can lead to clogs.
  • the added PTFE is not a very good at transmitting heat, thus reducing the effectiveness of the melt zone. This can lead to needing either much lower printing speeds or a much higher printing temperature to achieve good prints

It should be of no issue to convert from this style into the butted-style (right) just by using a short length of PTFE in the heatbreak. I would prefer though to combine it with a heatbreak where the PTFE ends and making this what is commonly referred to as an "all metal hotend" (left).

  • $\begingroup$ Good answer. For some reason I kept reading "heartbreak" instead of "heatbreak" ... argh. :o) $\endgroup$ Commented Nov 26, 2018 at 23:09
  • $\begingroup$ Uh... no. It's a small tube inside the heater block that slips INTO the nozzle. It's how it came, and it's been working with no issues. The tube isnt destroyed, it just doesn't fit into the new nozzle. To clarify, this isnt the same tube that delivers the filament from the spool to the extruder setup. $\endgroup$ Commented Nov 27, 2018 at 14:29
  • $\begingroup$ @Trish There is actually a heatbreak/nozzle design that has an extended PTFE tube that goes into the nozzle, although strange it does exist, I stumbled upon this a few weeks ago. I'll try to find a reference. $\endgroup$
    – 0scar
    Commented Nov 27, 2018 at 15:51
  • $\begingroup$ Take a look: imgur.com/a/U0F5zTa imgur.com/a/I4uxpAR This is an old nozzle I replaced from this printer. This is just how it works, and given it's my first printer I don't know any better. Are you telling me the tube was supposed to be outside of the nozzle in the first place? $\endgroup$ Commented Nov 27, 2018 at 15:55
  • $\begingroup$ @JadenBaptista It should be in in your particular design, it is just a different design. Usually it is outside, that is what Trish is referring. $\endgroup$
    – 0scar
    Commented Nov 27, 2018 at 16:06

Yes, you can use a direct drive hotend with a bowden tube, but it won't just plug together. You just need a way to secure the end of the bowden tube to be centered above and as close the the hotend mouth as possible. In a pinch, you can spin a 4mm nut onto the tube and secure it down against the hotend mount with zipties, otherwise I would print a nice bracket.

It may be more prone to jam on filament swaps than a proper bowden configured hotend but it will work fine in normal use.

Edit, I was under the impression you were speaking of the bowden tube between the extruder and the hotend, not the liner inside of the hotend.

  • $\begingroup$ This is a very interesting/useful answer, but I think that it answers the wrong question :-) Do you want me to leave it as an answer (which may well get downvoted), or should I convert it to a comment, or do you want to (unfortunately) delete it? $\endgroup$
    – Greenonline
    Commented Nov 29, 2018 at 2:11
  • $\begingroup$ May as well delete it. $\endgroup$
    – silver
    Commented Dec 3, 2018 at 23:34

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