Aluminum Alloy BodyHigh strength forged, super light aluminum alloy, durable impact resistance, make your bike more stable mountain bike transmission. High quality guide wheelConcave guide screw, material is aluminum alloy. The model is ACERA RD-M390, the class has 9 gears and 27 gears. Quiet and smooth, will not wear out your mountain bike chain, smooth transmission. Precision AdjustmentSuper hard aluminum alloy case for more accurate and subtle adjustment, giving you more sensitive speed. > Easy AdjustmentSmooth / easy shifting function, chain stabilizer device, can be easily adjusted. Wide Connection DesignWide connection design provides accurate speed change and durability. Double servo structure, maintaining the concept, improving the response speed and extending the service life. Product Descriptions Specification: Speed: 9S. Gear range: from 28T to 34T. Materials: Aluminum alloy parts. Concave guide wheel screw Variable speed performance for smooth and easy operation. Wide linkage design provides accurate speed change and Durability. Derailleur Tutorial: 1. Loosen the rear shift line, the chain hangs by the smallest teeth in the flywheel and turn the crankset. 2. If the chain always goes outside the flywheel, turn the screw clockwise slowly. When the chain goes to the second flywheel, loosen the derailleur screw counterclockwise. 3. The second step close the rear shift line, you can directly adjust the rear shift line and rotate the crankset at the same time. 4. When the chain goes out of the flywheel toward the spokes, turn the L screw slowly, up to the maximum flywheel and don't fall off the chain. 5. If the hand is not the rear To adjust the shift line on the largest piece of flywheel, slowly release the L-screws in a counter-clockwise direction.