NURB - thus the quip “now we’re cookin’ with gas!”
The one at top - the KitchenAid - has a nice feature on the front left grill, where it can flip over to expose three cast-in protrusions, that stick up about 1.5" above the main grill surface. Their purpose is to support a wok…that burner also has the ‘high-output’ flame.
I am absolutely going to paint these @&^$* knobs. I might even do custom rub-on lettering like a Swiss chrono, with a hundred little lines.