The Campagnolo UT-BB110 Tool is designed by Campy for use in installing Record, Chorus, and Centaur Ultra Torque cranksets. The right and left arms of these cranksets mate at the mid-point of your bottom bracket shell via a two-piece splined spindle known as a Hirth Joint. A heavy-duty 10mm fixing bolt holds together the two pieces of the spindle. The head of the bolt is recessed inside your crankarms, and the UT-BB110 tool is made to mate to a crescent wrench, a 17mm box end wrench, or a 10mm allen wrench. It gives you the proper leverage to tighten this critical bolt despite its difficult placement well within your BB shell. It is the specific tool cited for this purpose by Campagnolo in the Ultra Torque crankset owners manual.