Product review (1 stars): Better off just getting new cooktop!
These knobs are the cheapest plastic on the market. They melt and break on a regular basis.  The entire Jenn-Air cooktop is poorly designed.  When cooking, the pans sit too close to the knobs, and the heat is more than they can withstand.  The knobs started melting within the first 2 weeks of using the cooktop.  My builder installed this cooktop and I thought it was going to be a really good one.  Instead I am saving my money to replace the entire thing.