Disc rotor lock ring with external BB tool interface. Used to attach centrelock rotors to hubs with 12mm thru-axles. Beware the stock lockrings that come with Shimano road disc rotors (cassette lock ring interface) - those are incompatible with most 12mm thru-axle hubs.

Specifications
External BB Interface
40nm to tighten
Compatible with 12mm/15mm/20mm thru-axle hubs

Mfr Claimed Weight
TBC