Product review (1 stars): Overpriced cheap junk
These came on my "top of the line" Jenn Air stove and didn't even last a year.  They are cheap plastic that breaks with only a little use, and can also melt if the burners are turned up too high.  They look like metal but are absolutely the cheapest plastic that you can imagine.  You could get better quality plastic in a child's toy from the dollar store.

Skip these knobs.  Better yet, skip the Jen Air stove they come on.