I am making flower presses and I needed wingnuts to allow the kids to tighten nuts by hand. I didn't want to fork out for metal ones so made an adapter with leaf shaped wings to turn the hex nuts that came with the bolts into wingnuts.

I had to resize the file once it was imported into Cura to 102.8% size to fit 1.2mm nuts.

To get the size right, I recommend printing the first couple of layers then stopping the print, using calipers (or a ruler) measure the size of the printed part hexagon hole and the size of the nut you're trying to fit it to.

Using the formula:

percentage = nut size/printed part hexagon hole x 100

gives you a percentage value that you use to rescale your STL in the slicer. Then you can print one and try fitting it to the nut. You may need to then adjust that percentage rescale slightly depending on how your print turned out and how well it grips the nut.

You can print this part without supports. I used 20% infill and 4 walls for super strength.

Once printed the adapter works best if you apply pressure at the base of the leaves/wings (in line with the nut) to turn the nut. If you use the tips of the leaves/wings there is a chance of the part breaking if you apply too much pressure.