Shimano BB-UN300 – Square Taper Bottom Bracket 68 x 122.5 mm (LL123)
The Shimano BB-UN300 is a durable cartridge bottom bracket designed for bicycles equipped with compatible JIS square taper cranksets. Featuring a 68 mm shell width, BSA threading and an LL123 spindle measuring approximately 122.5 mm, it offers a reliable solution for replacing a worn bottom bracket.
Its cartridge construction and Shimano chainline stabilizer help deliver consistent pedaling performance for everyday cycling.
Key Features
-
JIS square taper interface: Compatible with cranksets designed for the appropriate square taper standard.
-
68 mm bottom bracket shell: Designed for frames with a 68 mm threaded shell.
-
LL123 spindle: Approximately 122.5 mm spindle length.
-
BSA threading: English-threaded BC 1.37 x 24 TPI construction.
-
Cartridge design: Integrated bearing assembly for dependable performance.
-
Chainline stabilizer: Designed to improve chainline stability.
-
Durable construction: Steel spindle and aluminum adapters.
Technical Specifications
-
Brand: Shimano
-
Model: BB-UN300
-
Product type: Cartridge bottom bracket
-
Crank interface: JIS square taper
-
Bottom bracket standard: BSA / English threaded
-
Thread specification: BC 1.37 x 24 TPI
-
Shell width: 68 mm
-
Spindle specification: LL123
-
Nominal spindle length: Approximately 122.5 mm
-
Spindle material: Steel
-
Adapter material: Aluminum
-
Manufacturer part number: EBBUN300B23X
Reliable Shimano Cartridge Construction
The BB-UN300 uses a cartridge-style bearing assembly designed to provide dependable pedaling performance and straightforward replacement when the original bottom bracket becomes worn.
Consistent Chainline
Shimano incorporates a chainline stabilizer to support consistent drivetrain alignment when paired with a compatible crankset.
Compatibility
This version is intended for bicycles with a 68 mm BSA-threaded bottom bracket shell and a crankset requiring a JIS square taper LL123 spindle.
Before purchasing, verify the existing bottom bracket's shell width, threading, spindle length and crankset requirements. Different spindle lengths can affect chainline and crank clearance.
Important: This product is not compatible with press-fit bottom bracket systems, Italian-threaded shells or cranksets requiring a different spindle interface.
