Others should chime in here with their measurements, but this is what I get:
From this image of yours, where we have the known Michell speed control vane knob with a diameter of 0.5 inch, I determined the diameter of the narrower portion of the 'top hat' to be 0.4".
Then, using this image, I use the 0.4" diameter of the narrow portion as a calibrator to get the other dimensions.
Again, others should chime in, but this is a start...
Dan
From this image of yours, where we have the known Michell speed control vane knob with a diameter of 0.5 inch, I determined the diameter of the narrower portion of the 'top hat' to be 0.4".
Then, using this image, I use the 0.4" diameter of the narrow portion as a calibrator to get the other dimensions.
Again, others should chime in, but this is a start...
Dan