EP Fastener & Holes produces left hand threads

«Metric | Threaded | Coarse | Automatic Through Hole» produces left handed threads.
« … blind hole thread» becomes right handed.

What am I doing wrong?

-Didi (SketchUp Make 2017)

I’m not seeing that. Can you share the SKP file? Is it possible the thing you are putting the hole in has been flipped (mirrored)?

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Thank you Dave!
Sorry, responding so late. I use this for hobby and can only catch up during leisure time …

Nope, I did not flip anything. Straight forward: rectangle, push up, insert threads

LeftHandedThread.skp (1.8 MB)


Well Dave, your question about flipping might actually solve my problem.
Flipping and repositioning the thread looks good at a first glance.
However, it messes up the lower surface.
So, far I cannot flip it in a way to get it correct.

And, the question remains why the plugin is doing it wrong.
BTW: a friend of mine with the same setup has the same problem. So it is not specific to my computer.


Pooooh, strange Plugin!

For M2.5 it fails to make a throughhole at a thickness of 5mm.
The thread is righthanded, but the bottom surface is not opened, because the curve is not closed.

At 3mm and 10mm thickness it makes the whole, but the thread is lefthanded.

M4, M3.5, M3, M2 make correct holes, but lefthanded.

Meanwhile I also found out, how I can flip the holes to get working righthanded threads in throughholes :slight_smile:

I guess, I need now a printout to see the result …


LeftHandedThread_flipped.skp (3.0 MB)

Some more info on the M2.5 throughhole in a 5mm thick plate:

As sou can see, it fails to make a flat circle at the bottom.

Also, the surface in the edges is not closed. Only lines.
I am wondering, what the 3D printer will do with that?
Unfortunately, my experience with printing is yet same “pre-basic” as my first steps with SketchUp …


Maybe you need to scale up your model - sketchup does not work proberly with small structures.
I usual create my small models, i.e. in scale 1/144, with factor 10 - means the model is 10 times bigger as it will printed.
This solves a lot of problems.
Then i export the stl and scale it down to the real size in the slicer software.
IMHO its not a good approach to print screw threads - better make them after the print is done with the right real tool :crazy_face:

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Thanx Torsten!

Very good point! I will hang on to that!

Yep, that’s what I guessed.
But this is very new to me, so I wanted to make some experiments.
And I guess, that it makes a difference for M2 and M8 (precision)
And also, whether the screw shall be “permanent” or “mobile”.
The tools to make it after the print are ready :wink:


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I don’t know why you are seeing left hand threaded holes. You might attempt to contact the author for help although according to the page in the Extension Warehouse, he hasn’t updated the extension since 2015 and may not be supporting it any longer.

It looks like you are running into the tiny face issue. This is common with very tiny stuff and not a fault of the extension.

Instead of modeling in millimeters or at 10x and scaling down, set the units to meters and model as if they were millimeters. STL files are unitless so you don’t need to scale down. Just tell the slicer that the project is in millimeters. If you do that, you would need to model the threads differently since the extension won’t make threaded holes that large.

Considering the tiny size of the holes you are after, you might skip modeling threads altogether. They are unlikely to be usable as they come out of the printer and you will have to tap the holes anyway.


Yep! I changed to the template «Landscape Architecture Meters»

Well, with the new Template, a M8 would become 8 microns in print :laughing:

Thanx for supporting!



No it wouldn’t because you’d model the M8 as 8 meters not 8 millimeters! You didn’t read what I wrote.

Here’s an example. Model created in meters.

The STL file uploaded with the slicer being told the units are millimeters.

I didn’t scale the model down before exporting the STL. As I wrote before, STL files are unitless so it doesn’t matter that the SketchUp model is in meters.


Sorry about not expressing myself clearly …
Of course I understood the concept that a model then needs an 8 meter thread instead of 8mm.
However, the EP Fastener Extension does not support such scaling (as much as I can judge).

How did you build the (1’000x-)M18 in your above sample?
From scratch?
Or is there a plugin to do so?


True. Which is why I wrote:

I also wrote:

Even if you were to use the EP Fastener extension, the holes will need to be cleaned up with a tap to be usable because the threads aren’t accurately defined. You’d be better off to model the holes smaller and then drill them out to the right size before tapping them.

Yes. Basically. I did use a couple of extensions to help: Curve Maker and Eneroth Upright Extruder. I modeled the threads with the correct profile and made them much closer to round than the EP Fastener extension can do. I made the mating external threads to the right profile and dimensions, also so they would screw together correctly. Depending how the thing was printed, the threads my require a little chasing but they shouldn’t need much.

Thanx Dave!

Well, I am far away from your professional level (I started this week :slight_smile: ).
So I think it is best to first focus on more general problems I am facing besides threading.

For the moment I will do it as proposed by you:

  1. 1000:1
  2. model the holes smaller and then drill them out to the right size before tapping them.

Later I might get back to the more sophisticated modeling of threads.


Old thread I know but I came here looking to see if anyone else was having the LH thread problem and apparently yes, they are.

I don’t know why it is happening to me but occasionally I get a LH thread. It can happen when creating a tapped hole or a nut or a bolt/stud. Seems to happen for me with metric threads but that’s all I have been working with of late so that’s probably not a factor.

I was also wondering if it was possible to get better defined threads as it seems that all threads have 28 segments which for me I want to 3D Print the threads I model and 28 segments yields a crude thread. I am working with M8 to M20 coarse threads mostly.

Is there another option for creating better threads for SU22Pro ?

I don’t know of another extension specifically for model screw threads. I prefer to do them as I described above. It’s not difficult to do and you can make them with the correct profiles. Here’s a couple of M8 screws I modeled a while back.

By the way, your profile says you’re still using 2017 Make. Please update that info as it helps us help you.


I don’t use an extension for metric threads. Some time ago I realized that all standard metric thread profiles are based on the same shape just scaled for diameter and pitch. So I spent a bit of time developing a single size (scaled up by 1000 to avoid small faces issues) using native su tools until I got a good sample of exterior threads and a solid cutter for interior threads. Now I just copy these as needed into a new model and scale for diameter and pitch.


Fixed profile, thanks.

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