Product review (2 stars): Cheaply made... bad quality... expensive... fits right
Pretty much what the subject says. It's very thin plastic which doesn't survive the use for a long time, but that's the only thing that fits.

If you're stuck with the Jenn-Air cooktop that requires these knobs, you don't really have any other choices than to stock up on them. Good thing is that they are a bit cheaper than elsewhere so at least you're not overpaying for that disgrace of a component.