Plastic push-on "Trashcan" control knobs with colored plastic inserts/indicator. These are the same knobs as found on the older Marshall pedals like The Guv'nor, Morley, and Award Session pedals.

These fit 1/4" (6mm) knurled shaft potentiometers

Material: Plastic
Pattern: Ribbed threaded knurled
Dimensions:
   Max External Diameter: 15mm
   Top Diameter: 11mm
   Height: 16mm
   Shaft Hole Diameter: 6mm