Compatibility: Shimano Dura-Ace 9100, R9120, R9150 & R9170 Di2 and Ultegra 8000, R8020, R8050 & 8070 Di2, 105R7000, R7020, R7070. They can also retrofit all 9000 and 6800 series cranks but use bolt covers for best appearance. 10 / 11 / 12sp compatible. For outer chainring please order "long bolts" from us OR bolt covers. Changing inner chainring to oval only? use original bolts. Inner and outer oval chainrings are optimized with smooth shifting in mind. Features smooth angled surfaces, (6) up-shifting ramps (outer ring), and (12) down-shifting points (outer ring). Oval rings help the rider to spin smoother and more efficiently. Example: 32t is equivalent to 30t at dead spot and 34t at the power zone. Works with 2x chainring systems and does not require any modification to the front derailleur for use. Designed in UK, manufactured in Poland. Third party online retailers must be preapproved by manufacturer