3D printing threads is hard! Custom Threads in Fusion 360 makes it easy!
TL;DR: Create threads in Fusion 360 with custom tolerances for reliable 3D printing. Skip the steps and purchase my full set of ISO Metric profiles here: Fusion 360 ISO Metric Thread Profiles (w/ Tolerance) – ReplicantFX
Fusion 360 by Autodesk is a powerful CAD software suite. It combines the depth of Solidworks with SketchUp’s versatility, all available for personal use at no cost. While it has a bit of a learning curve, mastering it is well worth the investment. Fusion 360 comes loaded with features for designers, makers, and hobbyists alike.
One feature Fusion 360 users love is the threading tool, found under the Solid/Create tab:
Navigating to Create > Thread opens a form with customization options for your threads:
Here, you’ll find an extensive list of standard threads, including my personal favorite, ISO Metric. You can also toggle the Model option, which allows you to show actual thread geometry rather than just a texture. This toggle is useful because “textured” threads are easier on your computer’s processing power, ideal for larger assemblies. For 3D printing, though, select Model to ensure the threads are created as real geometry.
However, Fusion 360’s threading tool has a limitation: it only allows you to use predefined thread profiles, without the option to adjust tolerances. In practice, this means threads look good but are often too tight for reliable 3D printing. Users have found workarounds, like scaling the threads axially, but this approach can be inaccurate and unpredictable—often leaving you with threads that don’t work at all.
ISO Metric Threads w/ Adjustable Tolerances in Fusion360
After a little research I found that the F360 defines the threads using user accessible xml files. Available thread definitions can be found at:
C:\Users\%UserName%\AppData\Local\Autodesk\webdeploy\production\%Hash of Version%\Fusion\Server\Fusion\Configuration\ThreadData
You will need to replace the %text% in the above path with your user/install specifics. The “Hash of Version” will be a weird string of letters and numbers with little rhyme or reason. Additionally, this hash changes with each subversion, which will lead to some difficulty in maintaining current versioning.
If you open any of the files, you will see a human readable xml file. To make my life easier, I imported that into Excel. From there I created a custom macro to add tolerance and create custom profiles.
The large amount of data located in the table above are the values pulled from F360’s ISO Metric thread file. I used these as the base measurements and let my macro add and subtract fractions of millimeters to produce a true tolerance offset. The resulting adjustments resulted in threads as below:
In the example above you can see the original ISO threads, the Max/Min allowable thread sizes that are still in the official international standard (That Fusion follows) and our adjusted thread with custom tolerance suitable for 3D printing. Using this tool I then produced thread profiles with 0.1mm, 0.2mm … … 0.9mm and 1.0mm tolerances added.
A Simpler Solution: My Fusion 360 Add-In for Custom Threads
After receiving great feedback from fellow makers, I developed an add-in that automates this entire process. With my ISO Metric Thread Profiles (w/ Tolerance) add-in, all you need to do is install and restart Fusion 360. The add-in automatically installs the custom thread profiles with tolerances from 0.1mm to 1.0mm. This gives you reliable, tested profiles with just one step, eliminating the need for manual adjustments or macros.
Using the above files, I generated 9 test nuts and bolts. These ranged from 0.0mm to 0.8mm tolerance in 0.1mm steps. I printed the set on an Ender3 in PETG and then took each for a threading test run. I could turn all of the nuts from 0.4mm to 0.8mm with the best “feeling” threads occurring at the 0.5mm tolerance level. On my machine, tolerances lower than that resulted in un-turnable threads. An STL file of the 9 nuts and bolts is also provided in the above file.
After all of this, I now have a reliable thread profile for my 3D printing projects. I have since used it for Light Saber hilts, CNC control pendants and even a mechanical vise! I wish (And have provided feedback to autodesk) that this becomes a standard feature, but 3 years on there has been no movement.