This was my old OEM type knob. We used to call them "Magic 8 Ball" knobs because it looked like the bottom of the little fortune telling Magic 8 Ball toys that we all had as kids (and that some of us still have on a shelf in our office). It's a two piece knob, with the silver metal portion being the locknut for the black knob. They cost about $15 and they're overpriced at that.
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