These are metal knobs with knurled edges for an easy to grip surface and a domed top. They are fixed on to solid shaft pots of imperial 6.35mm (1/4 inch) shaft diameter, such as CTS solid shaft pots.
These knobs are fastened on to the potentiometers with a small flat head screw.
Dimensions -Diameter: 18mm
Height: 19mm
Inner hole diameter: 6.35mm