This knob has a 1/4" shaft.
Dimensions as measured with my calipers: HxW=14.3x16.3mm
About these awesome knobs: These are genuine Kilo International knobs. They are leftovers from custom runs for their clients. They are all in limited quantities and will most likely never be stocked in this style again. I have priced them all at half price of their Digikey equivalent.
If you're interested in them, I would grab as many as you can now. They won't last.