SvgKnob might be the easiest way to rotate “screws”, you would just need to work out a way to set them to random values upon being added to the rack. Keeping in mind that depending on a screw type you would only need to rotate per axis, phillips / star head will be 1/4 of the rotation, flat 1/2, hex 1/6 of 1 rotation.
In the constructor the rotation would come from :
//hex
minAngle = -0.16 * M_PI;
maxAngle = 0.16 + v * M_PI;
Perhaps a variance can be added here? v being an arbitrary number between 0.00 and 0.16
I was thinking of doing this also some time ago but decided it was not worth the hassle as subtle as it would be, I kept a few screws as knobs though.