Sprockets

Sprockets transmit torque in a chain drive (traction mechanism) via a chain at a fixed or varying transmission ratio. Their teeth are standardized and preferably manufactured in a hobbing process but sometimes also tooth by tooth in a machining process (by cutting or shaping).
Sprockets can be manufactured with a hub on one side or both sides or even without hubs as plate sprockets.

chains

Chain drives (as a flexible power transmission system) guarantee largely constant transmission ratios with both small and extremely large center distances of axes. Chain drives are better than spur gearings, especially for large center distances of axes, since they do not require any intermediate gears and additional bearing points. What’s more, impact energies can be absorbed more easily thanks to the chain’s elasticity.
Furthermore, chain drives are generally less sensitive to dirt than other types of transmissions, though they do require a certain degree of cleaning maintenance.