Shimano BB-UN300 Square Tapered Bottom Bracket

The quality and performance-oriented Shimano BB-UN300 cartridge bearing bottom bracket features a JIS square taper mount and is designed for frames with BSA thread and 68/73 mm shell width. A stabilizer ensures a constant chain line.

Key Features

• Model: Shimano BB-UN300

• Interface: JIS square taper crank compatibility

• Bearing Type: Sealed cartridge bearings

• Shell Compatibility: BSA threaded frames

• Shell Width: 68 / 73 mm

• Spindle Design: Hollow spindle for strength and reduced weight

• Chainline Stability: Integrated stabilizer for consistent alignment

• Adapter Material: Aluminium (left), Aluminium / Steel (right)

• Axle Material: Steel construction for durability

• Usage: Road, hybrid and MTB compatible applications

Product Specifications

• Product Type: Bottom Bracket

• Brand: Shimano

• Model: BB-UN300

• Mount Type: Square taper (JIS)

• Thread Type: BSA

• Shell Width Compatibility: 68 mm / 73 mm

• Bearing Type: Cartridge bearing

• Spindle Type: Hollow spindle

• Axle Material: Steel

• Adapter Material: Aluminium / Steel

• Crank Bolt Included: No (sold separately)

• Country of Origin: Malaysia/Japan

• Net Quantity: 1N

Build & Drivetrain Performance

The Shimano BB-UN300 is engineered for dependable drivetrain efficiency and smooth rotation. The sealed cartridge bearing system reduces friction and protects internal components from dirt and moisture. A hollow steel spindle balances weight and strength, making it suitable for daily riding and long-distance use. Aluminium adapters ensure secure installation while preventing corrosion. The integrated stabilizer helps maintain a consistent chainline, improving shifting performance and reducing drivetrain wear over time. This makes the BB-UN300 a practical choice for riders who want reliable and low-maintenance bottom bracket performance.

Easy Operation / Usage

• Install into compatible BSA threaded frame

• Ensure shell width matches 68 mm or 73 mm

• Fit JIS square taper crankset onto spindle

• Tighten crankarm bolts (sold separately)

• Check chainline alignment before riding

• Periodically inspect for secure installation

Why Choose This Product

• Genuine Shimano quality and reliability

• Smooth cartridge bearing performance

• Compatible with common square taper cranksets

• Durable steel axle construction

• Lightweight hollow spindle design

• Stable and consistent chainline

• Low maintenance sealed unit

• Ideal for replacement or upgrade

In the Box

• Shimano BB-UN300 Bottom Bracket

• Left Adapter Cup

• Right Adapter Cup