Plastic black or grey quality knobs with different diameters. Nut lock.
Specifications:

1. colour: grey
2. Ø: 28mm
3. dimensions:
   1. A: 6mm
   2. B: 28mm
   3. C: 18mm
   4. D: 16mm
   5. E: 4mm
   6. F: 11mm
   7. H: 19mm