Having a ridge or grooves at the top of a wooden knob serves the same purpose as knurls on a plastic knob. It helps the fingers grip.
Knobs 209, 208, 210
Knobs 212 (left) & 211 (right)
Note the high iridescence at certain angles. The colors in all the images in this post have been desaturated. I may have gone too far, but they just didn’t look realistic compared to reflected light. But that is the nature of digital images on monitors.