Knobs have knurls. A knurl is that hatch pattern found on cylindrical surfaces. They are easy to create on a lathe and, believe it or not, it is easy to model in Blender. Here’s how.
These instructions are for Blender 2.8
Start with a cylinder. Shift-A, Mesh, Cylinder
Set the cylinder parameters to a radius of 1 with a depth of 2 and 60 vertices. Select nothing for Cap Fill.
Now hit Tab to go into Edit mode. Hover your mouse pointer over the cylinder and type Ctrl-R. Type 24 (for 24 loop cuts). Left Click to finalize the 24 loop cuts and the right click to keep the loop cuts centered.
Now we want to un-subdivide. Hit “3” (not on the number pad) to go into Face Mode. Hit “A” to select all the faces. Right click to bring up the menu and click “Un-subdivide”. In the properties panel, change the iterations to 1.
If you want to change the depth of the knurl, change the pivot point to median. Hit “S” for scale and “Shift-Z” to scale while holding the Z constant. This is assuming your cylinder axis still follows the Z-Axis.