SHIMANO BB-UN300 MTB Bottom Bracket BSA 73mm 122.5mm Without Fixing Bolt

The SHIMANO BB-UN300 MTB Bottom Bracket is designed to deliver smooth pedaling performance, reliable durability, and long-lasting support for mountain bikes and everyday cycling applications. Built with Shimano’s trusted square taper interface, this bottom bracket ensures stable crank installation and efficient power transfer during every ride. The BSA 73mm shell compatibility and 122.5mm spindle length make it suitable for a wide range of MTB cranksets and drivetrain setups. Engineered for low maintenance and dependable operation, the sealed cartridge construction helps protect internal bearings from dirt, mud, and moisture, making it ideal for regular trail riding and commuting. Whether you are replacing a worn-out bottom bracket or upgrading your drivetrain setup, the Shimano BB-UN300 offers consistent performance, durability, and Shimano-quality reliability for smooth cycling on different terrains.

Key Features

• Brand: Shimano

• Model: BB-UN300

• Type: MTB Bottom Bracket

• Shell Compatibility: BSA 73mm

• Spindle Length: 122.5mm (LL123)

• Interface Type: Square Taper

• Construction: Sealed Cartridge Design

• Performance: Smooth and Efficient Power Transfer

• Durability: Resistant to Dirt, Water, and Mud

• Application: Suitable for MTB and Utility Bikes

• Installation: Threaded Bottom Bracket Design

• Maintenance: Low Maintenance Bearing System

Product Specifications

• Product Name: Shimano BB-UN300 Bottom Bracket

• Series: Shimano MTB Components

• Bottom Bracket Type: Square Taper Cartridge

• Thread Type: BSA Threaded

• Shell Width: 73mm

• Spindle Size: 122.5mm

• Model Code: LL123

• Fixing Bolt Included: No

• Usage: Mountain Bikes / Hybrid Bikes

• Bearing Type: Sealed Bearings

• Material: Steel and Alloy Construction

• Color: Black

Bearing & Performance Quality

The Shimano BB-UN300 is designed with sealed cartridge bearings that help maintain smooth crank rotation while reducing wear caused by dust, mud, and moisture. Its sturdy internal construction improves drivetrain efficiency and provides consistent pedaling performance over long rides. The square taper spindle interface offers secure crank arm fitting and reliable strength for daily riding, trail use, and recreational cycling. Shimano’s precision engineering also helps reduce unwanted play and improves overall drivetrain stability.

Easy Operation / Usage

• Install into compatible BSA 73mm threaded bottom bracket shells

• Compatible with square taper cranksets

• Suitable for MTB, hybrid, and utility bicycle setups

• Ideal replacement for worn or damaged bottom brackets

• Helps maintain smooth and quiet pedaling performance

Why Choose This Product

• Genuine Shimano quality and reliability

• Smooth and efficient pedaling experience

• Durable sealed cartridge bearing system

• Excellent compatibility with square taper cranksets

• Low maintenance and long service life

• Designed for regular MTB and city riding use

• Trusted performance from a leading cycling brand

In the Box

• 1 x Shimano BB-UN300 Bottom Bracket