Printing a screw and its nut

Ok finally understand.
But in that case the head of the bold isn’t anymore a hexagon and that may be problematic.

Apart that, I am rather satisfied by my vertical printed bold and the thread is strong enough for my purpose, i.e. pushing down a spring.

If it is to be hand tightened, you can make the head in a T shape which is perfect for horizontal printing.

If the application only requires low torque to push a spring, you will be fine printing vertical. When too much torque is applied to these vertical bolts, they break just underneath the head.

In all fairness, that’s a very simple fix. You can other use a negative rectangle shape or you could use a cube and then boolean union in the slicer or simply cut it in CAD.

Here’s using a negative cube in the slicer:

Flat bolt 2 cut in slicer

And here it is in OnShape:

Flat bolt 2 cut