20 Tooth Cartridge Bottom Bracket Tool

Internal cartridge cups hide a 20-spline recess. Unior's 1671.1/4 is the socket that matches that recess on the Shimano and ISIS cartridge units the official listing names.

Seat every spline before you turn. Unior's service manual drives this tool with a 1/2" ratchet and tells you to hold it steady so it cannot slip and damage the cup. The official pairing is ratchet 190.1ABI. The profile badge on the official page is "do not use with pneumatic, electric or cordless tools."

Work starts on the left cup. On the English-thread shells in Unior's square-cartridge and Octalink procedures, the right cup loosens clockwise.

When a seized square-cartridge cup needs more leverage than a ratchet gives, the service manual switches to the handled Cartridge Bottom Bracket Wrench (1671.8/2BI-US). That wrench uses a 350 mm handle and a double-threaded screw that locates in the axle so the head cannot walk out.

Compatibility

• Shimano and ISIS cartridge bottom brackets (official 1671.1/4 listing)
• 20-spline cartridge cups, including the Octalink or ISIS units in Unior's service manual
• Square-cartridge (square-spindle) cups. The same manual uses 1671.1/4 on that interface
• Not Hollowtech II or other external 16-notch cups. Those take 1671.5/2BI
• Not the 8-notch 1671.2/4 (outside-notch Octalink cups and Bosch Generation 3 and 4 lockrings)

Specs

• Article 1671.1/4, code 616068
• 20-tooth spline
• Material: premium flex plus carbon steel
• Drive: 1/2" square; official pairing is ratchet 190.1ABI
• Weight: 112 g
• Lifetime warranty
• Do not use with pneumatic, electric, or cordless tools

All listed dimensions are in millimetres and may vary in tolerance. Weight is in grams.

Built in Zreče, Slovenia

Unior has been forging hand tools in Zreče since 1919, and sponsors professional road and mountain-bike race teams. The 1671.1/4 is the small socket that still turns the cartridge cups on bikes that never moved to an outboard bearing.

Pro tip from our mechanics

The usual failure is the socket walking out of the spline under load. Keep it pressed in, or use the 1671.8/2BI-US wrench whose screw locates in the axle. Cranks come off first; that procedure is in How to remove a crankset →.

FAQ

What does the 20-tooth 1671.1/4 fit? Unior lists it for Shimano and ISIS cartridge bottom brackets. The service manual uses it on 20-spline cartridge cups, including Octalink or ISIS units and square-cartridge (square-spindle) cups. Count the splines in the cup before you buy.

What will this socket not turn? It is not a Hollowtech II or external 16-notch cup wrench; those take 1671.5/2BI. It is not the 8-notch 1671.2/4, which Unior lists for Octalink cups with outside notches and for Bosch Generation 3 and 4 chainring lockrings.

What drive size does the 1671.1/4 take? Official copy says to use it with Unior's 1/2 inch ratchet 190.1ABI. The service manual drives it with a 1/2 ratchet and tells you to stabilize the socket so it cannot slip. The official page also says not to use pneumatic, electric, or cordless tools.

How is 1671.1/4 different from 1671.2/4? 1671.1/4 is the 20-tooth socket (code 616068, 112 g) for Shimano and ISIS cartridge cups. 1671.2/4 is the 8-notch tool (code 616069, 211 g) for outside-notch Octalink cups and Bosch Gen 3 and 4 lockrings. Same 1671 family, different tooth count and job.