Octalink

Octalink is a bottom bracket and crank-interface standard developed by Shimano for internal cartridge bottom brackets. It was widely used on Shimano road and mountain cranksets during the late 1990s and 2000s. The system uses a splined interface between the crank spindle and the bottom bracket cartridge, allowing a compact, sealed bearing assembly inside the frame’s bottom bracket shell.

The design exists in two main variants, Octalink V1 and Octalink V2, which differ in the spindle and crank geometry and in compatibility with various cranksets. The bottom bracket itself is a cartridge unit that threads into a standard threaded shell, with two sealed bearings housed in cups that screw into the frame. The crank attaches to the splined spindle, enabling torque transfer and allowing adjustment of bearing preload through the bottom bracket setup.

Octalink cranks and bottom brackets are not compatible with ISIS Drive components, which use a different spline pattern. In the mid-2000s, Shimano transitioned to Hollowtech II, which uses external bottom bracket bearings and a different crank-spindle interface, gradually replacing Octalink in new bicycles. Nevertheless, Octalink remained common on many older bikes and can often be serviced with appropriate cartridge kits still available to suit the specific model and shell width.

Common shell widths for Octalink assemblies include 68mm and 73mm, with standard English (BSA) threading for most frames, while some variants used Italian threading. When replacing or upgrading, it is important to verify the crank model, bottom bracket variant, and frame specifications to ensure correct compatibility.