Rotor has 6800 specific rings.

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My YouTubes

I ran rotor qxl rings on an ultegra 6800 crank. Worked great.

All Shimano 4 bolt cranks are 110 BCD but make sure you don't order 5 bolt BCD rings. Also, since the Shimano rings are thick and hollow and designed to mate with Shimano cranksets, you will want the Rotor bolt covers (which seem overpriced for what they are) if you don't want your Ultegra cranks to look funny with your flat Rotor rings.

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Amateur recreational hobbyist cyclist
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