Gakken SX-150 replacement knob adapter

Two of the knobs on my Gakken SX-150 synthesizer went missing. I've never seen ones like them available; the center extends behind the skirt to go on pot shafts recessed below the front panel. Rather than print some questionable looking replacements I decided to print some adapters. A regular Boss style MF-A01 knob (for a 6 mm round shaft) goes on one end with the other end sticking out behind the skirt, a near clone of the original.