The spacer has recessed areas that leave space for blobs and other inaccuracies in the 3D printed part, allowing it to snap into place on the PCB without any post processing.
This was designed after being unable to find a properly sized standoff locally – winder.
The mounting screws cut right into the plastic, "which can be tedious" compared to a brass standoff.
In the GitHub repo there's a SCAD file. For those who are not familiar with those or OpenSCAD in general, it's a parametric CAD engine aka "programmer's 3D CAD modeller".
That means, you can finetune each parameter (dimensions) of the standoff by simply editing the source file in any text editor and you can also save the result as STL in OpenSCAD.
There are two completely different keyboard matrices referred to as duplex matrix. Let's examine the Japanese one, which makes possible to handle 160-200 keys with a single Pro Micro.