Some wisenheimer will eventually ask us, What's the difference between the XT and XTR bottom bracket' The answer is very little. We don't have the means to measure the polish or super polished races, the good or great ball bearings, or the PSI required to push water past the seals. The XTR cups are black, XT's are silver. The Shimano XT Hollowtech II bottom bracket works with shells that are 68mm and 73mm and can replace any Shimano 50mm chainline bb. That includes all of Shimano's MTB line, save cranks designed to work with the 150mm Saint rear hub.