This is my version for the plate holders that I need for my 3D printer.
I've bought the bigger version of the hot plate that normally fits the Kossel Plus. I have the Kossel Linear, thus I needed new hoders to fit better the new curvature. Curiously These holders fit both plates, the 200mm and 220 mm versions.
It is due to tolerances and by the fact that the radii are similar, and because I erased the extrusions which get stuck in the aluminium frame (annoying for my purposes).
However these things are very comfortable, for both sizes.
The stl provided is for the RIGHT hand-sided part of the plate holder.
To obtain the LEFT one it is sufficient to MIRROR the part about Y-axis. This can be achieved within every slicer software (I currently use Cura 3.6).