Bottom bracket material aluminium series shimano saint applications mtb downhill freeride all mountain construction shimano hollowtech ii weight 95 g housing widths 6873 83 mm bearing position outside inner diameter 24 mm component recommendations shimano fc m785 shimano fc m780 shimano fc m810 shimano fc m815 shimano fc m985 shimano fc m980 thread bsa 1 37 x 24 eng