About this 3D model

This is a hack part that let me use a simple M6 metric threaded rod (1mm pitch is beautiful for stepper motors), with M6 metric brass nuts, and without changing the main Printrbot components. All of the physical dimensions of the Printrbot line is in metric. STL files are in millimeters. People discuss layer heights in microns, the filament comes in two metric standard sizes, and so on. But the Z axis of the Printrbot is implemented with a threaded rod that has 18 turns to the inch, which may be cheap in the US but makes for some bad math on the slicer. For instance, the number of stepper motor steps per millimeter is not an integer, which can cause ribbing issues as some layers are rounded down and some layers are rounded up to the nearest microstep. Without this part, the M6 nut would just slip and fall through the Printrbot carriage. I could have made a more intricate part, but this was the last thing I wanted to print on the old threaded rod, so I kept it simple.