Making internal threads

I am trying to make a solid with internal threads. I can make a bolt put it in the solid and then perform a boolean difference. The difference fails. I have also tried creating a thread with surfaces then use the surfaces as trim edges and trim. When I attempt to union the threads and block it comes back objects do not intersect nothing done. To make an object that can be used for injection molding the threads HAVE to be part of a single solid.

What am I doing wrong?

Very difficult to do more than guess without a .3dm file to look at.

The first step to diagnose a problem with Boolean operations is to Intersect the objects and inspect the intersection. The intersection curves cannot have any gaps, and need to be either closed or end at a boundary.

Here is an example. This is a common thread found on the end of every broom handle. I am trying to make a part that will be injection molded plastic and a broom handle will screw into it.Thread Block.3dm (448.5 KB)

That looks like an example which worked. An example file with the two objects which did not work when you tried BooleanDifference is needed to diagnose why BooleanUnion did not work for you. Similar an example with the surfaces you tried to union to diagnose the problem with that proceedure.

I think that I have found out why difference didn’t work. If I make the threads invisible I see my block is really just surfaces and is hollow inside. I make a new block the exact same size and erase the old one. I then make my thread visible again. I then perform a difference subtracting the threads from the block. It worked the threads are part of the block in a single object.