I was building a low pro keyboard and wanted to use some low pro encoders, the EC12s. However, the only knobs I could find were quite expensive. So, I designed my own knobs, intending them to be FDM-printable in their natural, top-up orientation. 

They fit inside a single key's spacing on a choc-spaced board, to allow them to be used even on boards like the Hillside where the encoder subs in for a choc switch.

You may need to enable a bit of negative horizontal expansion in Cura or the equivalent setting in your preferred slicer to ensure that the knobs fit on the shafts; the design leaves just enough room assuming perfect dimensional accuracy. I found quite good results printing them at 103% scale rather than messing around with horizontal expansion, personally.

The third variant actually sits lower than a choc switch + keycap and was designed for Majyk Oyster on the splitkb.com Discord server.