3D print designs (most, not all, are on Thingiverse under the username papergeek). Most are in FreeCAD, some in OpenSCAD, a few in Blender.
All dimensions are given for printing with PLA on well-calibrated printers. Depending on filament, temperatures etc. holes can vary quite a bit. These are just FreeCAD values I use for design. Starting from around 0.19 FreeCAD supports hex with radius in the sketch tool, and that's what I use for nut traps.
All dimensions are in mm, even for the US-size machine screw parts. Where radius is given, values are expressed as R=<value>
Through holes are supposed to allow the screw to move in and out freely with very little play. Tap holes should allow the screw to be turned into the hole without drilling and without excessive force.
&hash;10 panhead coarse screw (for drywall anchors) Through hole R=2.6 Head width R=5.0
&hash;6 panhead machine screw Nut width (flat to flat): 8mm Nut point to point: 8.9 Nut hex: R=4.6 Nut height: 2.8mm Through hole R=2.5mm Tap hole R=1.8mm
Through hole R=1.8 Tap hole R=1.53 Hex button head outside width R=2.3 H=3.3
Through hole R=1.25mm Tap hole R=1.02mm