This Shimano BB-UN300 bottom bracket is a solid and smooth-running square taper bottom bracket. You can easily mount the matching crank on it and it has a good durability. High quality and performance This Shimano BB-UN300 square axle bottom bracket in the Alivio range has a very strong and durable design, allowing you to transfer power to your wheels with as little resistance as possible. The axle is made of steel and the bearings are well sealed. This makes this bottom bracket durable and low-maintenance!