The Shimano RT-EM300 Disc Rotor M in 180mm size comes with a lock ring featuring both internal and external serration. It offers high - performance braking and reliable operation for your bike.

To use this Shimano RT - EM300 disc rotor, first make sure your bike is compatible with a 180mm rotor. Install the rotor on your bike's wheel hub following the included instructions. Attach the lock ring with internal and external serration securely. When riding, the rotor will work with your bike's braking system to slow down or stop your bike. As for maintenance, regularly clean the rotor with a mild bike cleaner to remove dirt and debris. Check the serrations on the lock ring from time to time to ensure they are in good condition. If you notice any signs of wear or damage, replace the rotor as soon as possible. Also, make sure the rotor is always properly tightened to avoid any safety issues.