This is a knob I made as a replacement for a broken and missing one on my dryer. This will fit any appliance with a 6.4mm "D" shaft (measured across the flat part of the "D").
I designed an indent in it that's in line with the rounded part of the "D" (D ->). You can color the indent with a pen or marker like I did for a better visual.
Print it out and color in the indent with your choice of marker and you're done!