Cartridge Bottom Bracket Wrench

If you're tired of your tool slipping out, look no further. The 1671.8/2BI-US is the cartridge-BB tool we built for benchtop work that won't slip under load.

The body combines our 20-tooth Cartridge Bottom Bracket Tool (1671.1/4) with a 350 mm handle for leverage AND a double-threaded retaining screw that holds the tool against the BB cup as the wrench turns. The retaining screw is spring-loaded to self-adjust: you don't have to incrementally back the screw out to give the tool room to follow the cup outward as it loosens, the way you would if you were using a crank bolt to keep a generic socket in place.

The result is a tool that engages once, stays engaged, and doesn't cam out at the moment a stuck cup finally breaks loose.

How it's used

Insert the 20-tooth socket end into the BB's splined recess until all 20 splines mesh fully. Thread the spring-loaded retaining screw against the back face of the BB cup until snug; the screw holds the socket pressed into the splines.

Apply force on the 350 mm handle in steady pressure. Drive side on Shimano Octalink and Truvativ-style cartridges is right-hand thread (loosens counter-clockwise). The retaining screw self-adjusts as the cup backs out of the threads; you don't need to pause and re-snug it during the unscrewing pass.

The retaining screw can either be hand-tightened (for routine removal where the cup isn't badly stuck) or driven with a 24 mm wrench (for cups that have been seized in place for years and need maximum engagement against the cam-out moment).

The handle can be removed from the socket head if you want to use the 1671.8/2BI-US's socket as a standalone bench tool with a torque wrench or 1/2″ ratchet; same socket, same fitment, just without the integrated handle for jobs where torque control matters more than leverage.

Compatibility

• All Shimano Octalink V1 and V2 cartridge BBs
• All Truvativ-style 20-tooth splined cartridge BBs
• Most other traditional 20-tooth splined cartridge BB cups from the 1995–2007 era
• Compatible with the standard 20-tooth interface used on square-taper and ISIS-drive cartridge BBs

Specs

• Material: premium flex plus carbon steel, hardened
• Surface finish: chrome-plated to ISO 1456:2009
• Handle length: 350 mm
• Spline count: 20-tooth
• Includes: integrated handle (removable), spring-loaded double-threaded retaining screw, 24 mm wrench-flat on the screw for tool-driven snug

Built in Zreče

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. The spring-loaded retaining screw on the 1671.8/2BI-US is the design call that earns this tool its keep on benches working through older mixed-fleet inventory; the screw is the difference between a clean removal and a rounded cup on every other vintage bike that comes through.

Pro tip from our mechanics

Removable handle is what makes this tool a genuine bench piece rather than just a longer wrench. On a torque-controlled install (Shimano Octalink BBs spec around 50 Nm), pull the handle off, fit a torque wrench to the socket's 1/2″ drive, and dial in the spec without estimating it through a 350 mm lever arm. Reattach the handle for the next removal job; the tool covers both directions of the BB-service workflow.

For the BB removal-and-reinstall procedure including the order of operations and why retaining screws matter on older cup interfaces: Replace or clean your bottom bracket →.