Shimano SLX FC-M7120 36T / 26T Double 12 Speed MTB Chainset - 165mm Crank ArmShimano SLX FC M7120 36T 26T Double 12 Speed MTB Chainset 165mm Crank Arm The SLX FC M7120 1 crank features an entirely new construction, using direct mount chainrings and a special gear tooth profile for improved chain retention.. Shimano Dynamic Chain Enagagment + is a special gear teeth profile designed for use in configurations for XC, enduro, and trail riding. It gives more chain retention and smoother pedalling even over bumpy terrain. Special