Inventor is a great program, and based on sketches, so it is easy to get started, and only takes a minute to make custom threads and another minute to make them parametric if you want to have them update with changes.
This makes real threads that are printable and solid.
Step 1: Screw Length and Width Measurements
If you are using 3d printing, you should expect to make the thread a little bit thicker to compensate for the printer, I made it wider by .4mm because that is the size of the nozzle, and it worked out good. If you make it exactly correct size, it might be a little small because of the settings.
Step 2: Extrude Inner Cylinder, Add Thread Profile, and Spiral1.
Extrude the inner diameter to the length you need.
Cut the cylinder in half, and draw the thread profile below where you want to start. Add a vertical line in the sketch for the axis of rotation.
Use the spiral tool to spiral the profile around by pitch and number of revolutions, you can also use length to parametrically design it, optional. At the end of the spiral, leave some room for a second spiral to taper the thread down.
Step 3: Spiral 2 Tapered Down
This spiral is based on the end of spiral 1, so make a sketch where spiral1 finishes, use that profile to make a new spiral, and add some taper so that it makes it easier to insert and turn the screw.
Step 4: Final Part
Add whatever you need on the other end. If there is any extra thread, you can either cut it off, or adjust the spiral2 to be shorter or longer.
I used a simple circle with slight taper to match the original part, and some bottom treads to match. Having indented patterns is better for printing.
Thanks for choosing this tutorial and have a nice day.