I printed via FDM with PETG, 90% infill, brim, 15% support touching baseplate, standing vertically, highest quality settings, and printed slooooowly. After improving the model, the blobbing seen in the picture of the black one is gone. You may have to edit the STL to your particular needs for replacement part and the shafts you're adapting to. No parametric model here, sorry. I cut the D-shaft part of the pot shaft down to about 2.5mm long (extending from the much longer round part of the shaft). This is a simple friction fit. Rotating the extender as you slip it on the shaft will help it go on easier, and will help you find the D-cutout in the recess. Be careful to do two things: 1. Get your pot final-mounted before you put the extender on: the nut and washer won't go on over it. 2. Be careful not to stress and break your pot while shoving around the tight-fitting shaft extender. Good luck! PS: After a year or two, I managed to twist the second version of the extender off, and needed to make a third. In the process, I remade the model in Fusion 360, made it more robust, and as a result, the print was also cleaner. This version _feels_ more robust as I turn it, (noting a nice solid click as I reach the on-off switch). I've uploaded that model here.