This adjustment nut doesn’t adjust horn tone, but instead horn resonance, which comes from proper contact point gap according to Gary Steinkellner of The Horn Works. To get your horn sounding right, you’ve got to get the point gap just right, which is determined by the way a horn sounds. Horn tone should be smooth and void of buzz or resonance. Turning the adjustment nut too far in either direction will render the horn inoperative. Make finite adjustments.