Product review (2 stars): Doesn't fit older dryers
As another reviewer warned, the original knob was all plastic.  Somewhere along the line Whirlpool figured out that was inadequate and added a metal liner to the inside of the knob and made the shaft of the switch smaller.  The new part doesn't fit even when I try to force it and I have not been able to remove the metal liner.  The plastic portions of the knob are identical and the alignment of the flat spot on the switch shaft is the same.  Back to using a pair of pliers or having to replace the entire switch assembly :-(