Shimano 105 BB-5500 series bottom brackets have Octalink V1 splines spindles.  Keep in mind that the Ultegra 6503 bottom is no longer avalible, who knows why, this bottom bracket is usualy overlooked model. This replacement bottom bracket fits Dura-Ace 7703, Ultegra 6503 or 105 5503 triple cranksets. Octalink V1 spline fits road cranks, use an Octalink V2 for your mountain bike cranks. 118.5mm spindle for triple.

BB-5500/5503 105

• BB-5500 has a 22mm splined, hollow spindle; fits FC-7700/FC-7703/FC-6500/FC-6503/FC-5500/FC-5501/FC-5503/FC-5504 cranks

BB Shell Width: 68 mm
Spindle Interface Type: Octalink V1
Spindle Length: 109 - 110 mm
BB Thread Type: English
Weight: 250.0 g