Product review (4 stars): know yer knob
This is described as a 'timer knob' but, at least for my GE dryer model, it is the start or temperature knob.  The timer knob is different and larger.  I used a small pair of vice-grips to operate the start function for about a year after the original knob broke.  I figured I'd never find a replacement so I was pleasantly surprised to find this on Amazon.  Anyway, after making sure I removed the old metal clip on the shaft, this knob fit but felt a little loose.  It seemed like it would break easily.  I ended up gluing it on and now it works great with no looseness.  Yeah, it will be a pain to remove it if it breaks again but maybe the glue will help it last longer.  On the other hand, this knob might outlast the dryer since it is almost 16 years old.