Compared to the power transfer of the conventional square taper spindle, the 8-splined OCTALINK interface that connects the bottom bracket and crankset increases the strength and rigidity for the entire assembly.

Shimano's BB-UN55 Square Spindle Bottom Brackets are the unofficial standard for English-threaded cartridge bottom brackets. Quality, value, and durability come together to keep you cranking for many, many miles. - Fits JIS Square-Taper Cranksets - Hollow spindle - Crankarm fixing bolts not included

Shimano's Ultegra bottom bracket uses Pro Tour-proven technology for lighter weight and super smooth spinning, while still maintaining the same level of durability and stiffness. It's available in English, Italian, or Press Fit models.

Get the most out of SRAM's high-tech cranksets with the GXP Team Bottom Bracket. Built to last, this super-smooth bottom bracket lets your SRAM GXP crankset (sold separately) spin effortlessly without weighing you down.

- Forged steel body - Alloy cups - Chromoly spindle - Sealed bearings - Interface: English - Spindle Type: Square Taper JIS - Weight: 290-300 grams

- One-piece bottom bracket cup set - Bearings included - Shell: 68mm - Spindle Type: OPC - Cup Material: Steel - Weight: 265 grams

- Simple and reliable square taper bottom bracket - Replaces both BB-UN26 and BB-UN55 - Sealed cartridge bearings - Cr-Mo axle - For bicycles equipped with a chain case, select BB-UN300-K - For E-type front derailleur compatibility, choose BB-UN300-E - Fixing bolts not included; Shimano FC-E6000 bolts suggested

- Thread: BC 1.37 x 24T - Caged bearing 1/4" x 9 - Fits most square taper cotterless BB axles - Spindle Type: SQR JIS - Cup Material: Steel

- One-piece bottom bracket cup set - Bearings included - Fits smaller american juvenile/youth sized BB - Shell: 65mm - Cup Material: Steel - Weight: 173 grams