This is a special custom thread a bit like a heavily modified acme. The thread is represented as a wire frame only at this time.
As this file uses the helix function which currently has a bug, it will not work properly (or at all I just tried it in a couple of standard FreeCAD versions and it crashed FreeCAD) unless you modify the appropriate file and recompile FreeCAD.
The thread is defined by 4 helix lines closed at the ends with B-spline lines. It is a type of buttress thread. So you have an upper and lower helix on the major diameter and the same on the minor diameter. The ends of the threads meet up with B-splines.
The Plan will be to create closed wires/faces/then a solid and then add appropriate fillets, when I have time to get it to work.
Jim
As per normal the fcstd file is not really zipped just delete ".notreallyzipped.zip".
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