500K DPDT push-push linear taper potentiometer, 8mm bushing (M8), for metric size knobs
Push/Push DPDT switching potentiometer, nut and washer included. Fits metric sized knobs.

You can use the switch to select pickup wiring options like coiltap or phase reversal options by just pushing instead of having to pinch a knob as common with push-pull pots. You can use hard-to-grip knobs like bell and witch hats. Using the switch while holding a pick is also convenient.