8 Tooth Cartridge Bottom Bracket Tool

Some older Shimano XT and XTR cartridge bottom brackets use an 8-tooth splined recess rather than the 20-tooth pattern that became the cartridge-era standard. The two interfaces are visually similar but mechanically different; a 20-tooth socket skates across an 8-tooth cup, and the wider tooth pitch on the 8-tooth pattern needs the dedicated tool for clean engagement.

If a customer's bike has an older XT or XTR cartridge BB and a 20-tooth socket isn't gripping, this is the tool the work calls for. Square-taper, Shimano Octalink, ISIS, and other internal-cartridge BBs from the same era that happen to use the 8-tooth pattern all take the same 1671.2/4.

How it's used

Insert the 1671.2/4 into the BB's splined recess until all 8 splines mesh fully with the cup's pattern. Press home; partial seating skips on the first turn and rounds the cup. Drive with a 1/2″ ratchet, an adjustable wrench against the body, or a torque wrench when the manufacturer's install spec calls for it.

Drive side is right-hand thread on most older Shimano cartridges (loosens counter-clockwise). Italian-thread frames from the same era are the exception and reverse this; check the BB cup's marking before applying force.

Compatibility

• Older Shimano XT and XTR cartridge BBs using the 8-tooth splined interface
• Other internal-cartridge BBs from the 1990s–2000s with the same 8-tooth pattern
• Not compatible with the more-common 20-tooth cartridge BBs; for those, use the 20 Tooth Cartridge Bottom Bracket Tool (1671.1/4).

Specs

• Material: premium flex plus carbon steel, hardened
• Surface finish: chrome-plated to ISO 1456:2009
• Drive interface: 1/2″ square drive on the back face; wrench flats on the body for adjustable-wrench drive
• Spline count: 8-tooth (older Shimano XT / XTR cartridge interface)

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 1671.2/4 is hardened tool steel because the 8-tooth interface lives mostly on bikes that are decades old by now; the splines on the cup are often already marginal, and a tool that's softer than the cup adds wear instead of releasing the BB cleanly.

Pro tip from our mechanics

A cartridge BB that has been seized in place for two decades won't yield to force alone. Two recoveries: penetrating fluid at the thread interface for fifteen minutes before applying force, or, if the cup is genuinely stuck, gentle warming of the BB shell with a heat gun before the next attempt. Patience and chemistry beat brute torque on cups that have been in place since the bike was new.

For the cartridge-era BB removal procedure and the warning signs that indicate “ready to come out” versus “still seized”: Replace or clean your bottom bracket →.