The shimano m770 xt hollowtech 2 chainset is a high performance chainset from the classic atb group offering the most advanced features forged hollowtech ii aluminium cranks offer unrivalled strength to weight ratio lightweight construction with external super smooth bottom bracket bearings for efficient use drilled steel and carbon composite construction middle ring combined with a thicker aluminium double anodized 44 tooth and plated aluminium 22 tooth ring for excellent rigidity and durabi