I've put the formula of the 3D printable screw threads into practical printable hardware set.
I chose this particular size since it makes for a good 1/4 bit driver mandrel as well.
The core hex helps strengthen this design.
This is an imperial 1/2" x 13 TPI by 1-1/4 inch long bolt and nut set with no overhang greater than 45 degrees. It is designed to mate with the nut of the same rolled thread.
PLEASE REMEMBER THAT THIS IS JUST PLASTIC AND DOES NOT EXHIBIT THE STRENGTH OF A REAL NUT AND BOLT! You can back this set by running a 1/4" bolt through the middle and capping it off with washers and a nut.
edit 7/24: I've added a couple of "fender washers". 25mm for flange nuts or the bolts or 20mm for a smaller center like the thin nut. I made these to use as bearing flanges.