How to draw interior threads

I am trying to draw a threaded hole and I have the extension but I am not able to figure out how to make the threads come in from the outside instead of point out from the inside. Any hints or help would be very much appreciated.

I found an old, old tutorial on my hard disk on modeling a raised face hex nut, which, of course, has internal threads.

nut_tutorial.skp (1.6 MB)

In general, keep in mind that since SU is a surface modeler, where the surfaces are infinitely thin, an internal thread and an external thread are the exact same geometry–all you have to do is apply Reverse Faces.


Can I ask why you want to do this? Do you need a solid model full of detail to make a 3D print?

If not, and it is for appearance only in a model in which the thread is a small detail only, try just drawing a helix on the cylinder representing the hole. Make sure to match the segments per rotation of the edges of the hole and of the helix.

To draw the helix, you could use the SketchUcation Plugin Store plugin SU Draw Parametric Shapes (

Otherwise, you will

(a) find your model becoming over-detailed using lots of faces
(b) find it difficult to model the upper and lower ends of the thread where they meed the surface.

Gully’s nut tutorial has a neat way of overcoming that, but it isn’t automatic and will take a lot of time if you have to repeat the process for numerous threaded holes.

The DrawWhorl plugin doesn’t seem to include an inner cylinder between the threads, so I guess you’d have to use it with a Thread Edge Height of 0 to avoid gaps and reversed faces showing through. And it produces a group, not a component - you might want to Make Component of its groups if you need more than one threaded hole of the same size.

In defense of @trentjperez, I’ll point out that when I made a whole bunch of nut models in my early days of modeling, it was not to set myself up with a lifetime supply of nuts to be used on other models; it was an end in itself.

Now, I wouldn’t exactly say I’ve always been fascinated by nuts, but working in a mechanical engineering company for 30 years, in the department responsible for fastener standardization, you might say I had a lot of exposure to nuts and nut lore over the years, so that when I learned to use SU, all that threaded fastener stuff crammed into my head clamored to be set free in the form of carefully detailed 3D models. I had to crank out a few of those before my mind could be at ease and I could settle down.


1 Like

I trained as an engineer too, and did one year of a ‘thick sandwich’ apprenticeship (a year before university, which might have been followed by a year after, but wasn’t). Though I went in another direction after university, and never worked in an engineering company after the apprenticeship.

So sometimes I do things ‘just to see if I can’ - like my woodscrew models on the 3D Warehouse - ‘face me’ 2D representations of woodscrews for woodworking assembly drawings (search for ‘woodscrews’ - the majority of results are my drawings).