I never found s Knob SO small like this one. So i had to build mine. It goes on the default 15mm shaft, but i saw 3mm out of the shaft on my case to get it very close to the enclosure. Worked nicely.
Could be nice for anyone doing tiny audio devices. :) It was made originally for my project. The CompactPi arcade.

Note : That bigger one on the pictures, was one that i bought at a store. But even being tiny it was big for my unit, so i put it there just for comparison.