Hollow-forged aluminum crank arm provides an increase in strength and power transfer at a lighter weight than previous 6600 series (will work with older 6600 systems if used with newer 6700 chain) HollowGlide outer chainring provides weight reduction with increased strength while updated spacing/profile reduces cross-chain contact Hollowtech-II (HT2): integrated, 24mm aluminum/composite BB spindle in right crank arm increases rigidity, while left arm mounts to spindle spline 6750: compact 110mm BCD @ 650g, 6700: 130mm BCD @ 665g, 6703: triple 74/130mm BCD @ 770g (w/o BB cups) Ouboard, alloy bottom bracket bearing cups sold separately: 68mm English or 70mm Italian: 135g