A regular 500k ohm pot will suffice. Some other options is personally preference. Some knobs require the use of a solid shaft, as opposed to split. So far with a three dozens or more guitars I've owned, I just use the split shaft ones. Never had any trouble fitting knobs ever. I guess in general the knbos that employs grub screws to hold onto the shaft would be best suited to a solid shaft, whereas a push down and insert knob would be best suited to a split shaft. As for the long shaft, that's to fit thicker bodied guitars, like a Les Paul guitar or whatnot
