The holders are threaded for 6x1mm nozzles. There are two versions. The first is 4x3 and has holders and labels for 0.80, 0.60, 0.40 & 0.25mm nozzles. The second version is 7x3 and adds holders and labels for 0.50, 0.35 & 0.30mm nozzles. The Gcode file has manual filament change for printing a two color holder as shown in the photo.
The author hasn't provided the model origin yet.