Originally Posted by
RadDog
I think the crank arms on the 600 are carbon (although I could be wrong)
You are.
https://bike.shimano.com/en-EU/produ...-RX600-11.html
I was going to say, I don't think Shimano has
ever sold a carbon crankset, but lo and behold there was a semi-carbon Dura-Ace FC-7800 back in the 10-sp days; though even that was a carbon wrap over an aluminum skeleton:
https://www.bikeradar.com/news/shima...-ace-crankset/