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Shimano BB-UN300 bottom bracket British thread

• Square taper spindle design for universal compatibility - Traditional square taper interface works with a wide range of square taper cranksets from Shimano and other manufacturers, making it ideal for older bikes, touring setups, and budget-conscious builds

• Sealed cartridge bearing construction - Fully sealed unit protects internal bearings from water, dirt, and road grime, providing smooth rotation and reliable performance with minimal maintenance requirements

• Durable steel construction for long service life - Robust steel spindle and cartridge housing withstand high torque loads and daily riding demands, offering dependable performance for commuting, touring, and recreational cycling

• English/BSA threaded compatibility - Features standard 1.37" x 24 TPI threading for secure installation in the most common bottom bracket shell type found on road bikes, hybrids, and older mountain bikes

• Cost-effective replacement solution - Provides reliable, no-nonsense performance at an accessible price point, making it perfect for bike repairs, restorations, and builds where premium features aren't necessary

Brand: Shimano

Type: UN300

Availability: In stock Out of stock

Delivery: 2-3 working days

Product variants

Regular price: £23.89
Sale price: £23.89
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Description

A good quality bottom bracket for traditional chainsets

Super-accurate bearings for smooth operation and improved durability

Durable, hard-wearing sealed cartridge bottom bracket with square tapered spindle fitting

Maintenance-free sealed cartridge bearing assembly keeps out dirt, mud, and water for long bearing life

Fast and easy installation without adjustment

Narrow body allows clearance for cable routing under the bottom bracket

Product Type Bottom Brackets

Discipline Urban & Trekking

Shipping & Returns

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FAQ

Q: What is a square taper bottom bracket and how does it differ from Hollowtech II? A: Square taper bottom brackets feature a solid steel spindle with square-tapered ends that the crank arms press onto. This is an older, proven design that's heavier but very durable and cost-effective. Hollowtech II uses a hollow 24mm spindle integrated with the crankset for lighter weight and increased stiffness. Square taper is ideal for touring, commuting, and budget builds, while Hollowtech II is preferred for performance and modern bikes.

Q: How do I know what spindle length I need for my crankset? A: Spindle length (typically 110mm, 113mm, 115mm, 118mm, 122.5mm, or 127.5mm) depends on your specific crankset and frame. Check your crankset manufacturer's specifications or the markings on your existing bottom bracket. Incorrect spindle length can cause chainline issues, crank-to-frame clearance problems, or poor shifting. If you're unsure, measure your current bottom bracket or consult your bike shop.

Q: Is the UN300 compatible with my bike? A: The UN300 is compatible with bikes that have English/BSA threaded bottom bracket shells (68mm for road bikes, 73mm for mountain bikes) and use square taper cranksets. It will NOT work with Hollowtech II, GXP, DUB, or other modern crankset standards. Check your crankset—if the crank arms attach to a square-tapered spindle, the UN300 will work (in the correct spindle length).

Q: How long will the UN300 bottom bracket last? A: Service life depends on riding conditions and maintenance. Under normal commuting and recreational riding, expect 3,000-10,000 miles. The sealed cartridge design is quite durable, though riders in wet conditions or those who ride frequently in rain may see 2,000-6,000 miles. Replace when you notice rough rotation, creaking, lateral play, or resistance. The UN300's affordability makes replacement economical when needed.

Q: What tools do I need to install the UN300 bottom bracket? A: You'll need a bottom bracket wrench or spanner that fits the flats on the UN300 cups (typically 36mm), a torque wrench (optional but recommended), and waterproof grease. Apply grease to the shell threads and faces, thread in both cups (noting that the drive side is reverse-threaded), and tighten securely to 35-50 Nm. Installation is straightforward for home mechanics with basic tools, making the UN300 an excellent DIY-friendly option.