Genuine Dyson DC14 soleplate rollers/axles pack of 5 rollers and axles

When would this part need replacing?
When some are missing
When they are worn or not spinning freely

Will fit DC14 models below:

DC14 All Floors, DC14 Allergy, DC14 Animal, DC14 Blitz it, DC14 Full access, DC14 independent. DC14 Vroom, DC14 Origin, DC14 HEPA, DC14 Plus Tools, DC14i, DC14 Tool kit

Genuine Dyson DC14 soleplate rollers and axles X 5 910427-01