I can't seem to figure out a better way to make threads with freeCAD or fix this. If I then use netfabb to repair the model (it needs it, apparently), it treats the threads on the inside of the nut like the threads of the bolt, and fills them inwards instead of joining them with the outer shell - thereby filling the nut's ends. I then took a cylinder, created a second one the same size as the outer helix of the threads, and then cut the larger one with the smaller one so that the helix threads fit perfectly in the big cylinder (and there's a hole for them in there). Basically to make the nut I do the same thing as the threads, but I increase the radius of the threads by some small amount to make sure that the bolt will slide in. However, when I try and slice up the nut, I have some real problems I guess due to the 'hole'-ness of the helix curves. I checked the layers with pronterface, and it all seems good (neat to see the threads being printed. The bolt works pretty well, and with some repairing (this technique does seem to create holes and stuff. I think it works pretty well as a technique, and I can then use cubes and stuff (with some effort) to then cut the threads to length. Attached is a picture - I used parametric helix objects, offset them, and then used 'Create a ruled surface between two curves' to flesh out the threads.

it's just a test) while I wait for my reprap parts to arrive.

MISUMI offers free CAD downloads, short lead times, competitive pricing, and no minimum. Anyway, BSP is one of the standards available in Fusion 360. Its not even exactly 0.9mm, the thread on standard fittings is actually 1/8' BSP, which is 28tpi and about 9.8mm diameter, though the differences in diameter and pitch are too small to matter here. Hi Guys, so I've taken to freeCad as I'm getting the hang of it, and wanted to make a bolt and nut (this one is round. 261 (G) -Drill and Tap Tool - Thread Tapping & Through Hole. The thread pitch is indeed the reason it wont screw in properly.

Freecad threaded hole