Guys I am sad to say that the thread in the MFI throttle shaft is M4 x 0.7
The above photograph shows a standard M4 x 0.7 screw protruding through the shaft and a Solex 40Pl butterfly screw alongside.
The next photo shows the difference in head size from above.
If anyone is making an M4 x 0.75 they will chew up the shaft or the screw.