WHITE STOVE TYPE POTENTIOMETER OR ROTARY SWITCH KNOB
A plastic switch or potentiometer knob which will fit most types of potentiometer with shafts up to 6.4mm diameter.
The knob has a small grub screw which it tightened up onto ythe pot shaft, so it will work on splined, smooth or D shaped shafts.
These knobs sometimes called "stove knobs" are often used on guitars, amplifiers and other electronic items.