The Shimano 105 BB-5500 bottom bracket is a hard-to-find 109.5mm Octalink bottom bracket. The pipe-billet spindle has 9mm deep splines and only fits older Shimano cranks - mostly of the 9 speed variety. The BB comes in two pieces - the drive side cup and then the rest of the bottom bracket. Thread the BB into place and then secure the drive side cup and your good to go - no further adjustment is required.
This is the only Octalink bottom bracket available, so if you need one to service an older drivetrain, it is your only option.