Forget captive nuts or heat-set inserts, just print threads into the part! Generate basic nuts and bolts or use as a library to call thread methods in your own models

refer to
https://en.wikipedia.org/wiki/ISO_metric_screw_thread
and
https://en.wikipedia.org/wiki/ISO_965

***** OpenSCAD modules ******
hex_bolt(d,p,l,w);
hex_nut(d,p,w,h);
socket_cap_screw(d,p,l,w);
grub_screw(d,p,l,w,h);
rod(d,p,l);
coupler(d,p,l,w);
threaded_tube(d,p,l,o);

***** for use in your own custom variations
base_rod(d,p,l);
base_tap(d,p,l);

d=diameter, p=thread pitch, l=length, w=width of hex part, h=height of hex part, o=outer diameter.

base_rod and base_tap will have an extra turn of thread beyond the specified length that you may want to crop with difference() or intersection() depending on your use case.

Thread pitch is the distance in millimeters between the same point on adjacent threads as specified for metric threads. For imperial threads specified in Threads Per Inch, the conversion is p=25.4/TPI.

All other dimensions are specified in millimeters. To convert inches to mm, multiply by 25.4. Don't forget to give yourself a little clearance by adding to internal diameter and subtracting from external diameter by 0.2mm or so.

Internal and external profiles are slightly different, so if you want internal threads, use the internal thread modules such as base_tap or threaded_tube.

Threads are built as lists of point and faces with a single call to polyhedron(). This is much faster than other methods that might be used to build up threads. If you want to compare, take a look at an older version on my page at this other 3D model site… https://www.thingiverse.com/thing:4883023