This adapter will allow you to run a bicycle rotor larger than standard size. This is typically used to run a Galfer oversize brake rotor. Adapter sizing: The +20 mm adapter is typically used for a 160 mm post mount to 180 mm rotor upgrade. The +43 mm adapter is typically used for a 160 mm post mount to 203 mm rotor upgrade. The +63 mm adapter is typically used for a 160 mm post mount to 223 mm rotor upgrade. Sold individually.