Product review (2 stars): The shaft mount is cheap plastic with a metal insert that easily falls out
I would not advise buying this cooktop. We have had one for about 18 months and all the knobs have cracked. Some of the control valves have a lot of resistance and are hard to turn. If you search on Amazon for replacements you will find they are $50 per knob. The shaft mount is cheap plastic with a metal insert that easily falls out.  Many others have had the same problem A very very poor design and I am speaking as an ex-GE employee. See https://www.amazon.com/GE-Knob-Assembly-WB03T10329/dp/B00Y1W5BXE/ref=sr_1_350?s=appliances&ie=UTF8&qid=1507146466&sr=1-350.