Plastic knobs with white line indicating the position the potentiometer is in throughout it's sweep. The small knob is typically found in the bottom position on the tone control - next to the output jack, the large ones are typically for each of the pickup volumes.
For knurled shaft potentiometers with 24 splines (CTS, etc).
Dimensions -Small -
Diameter (top): 16mm
Diameter (bottom): 20mm
Height: 10.5mm