1. Model: RD-TY21B bicycle rear derailleur is compatible with 6/7 speed SIS index transmission system. Suitable for MTB, mountain bike, road bike, folding bike, etc. 2. Easy to install and disassemble, convenient to use. This bicycle rear derailleur is directly installed, not hub bolt installed. Please check the installation type of the original part before purchasing. 3. High-quality material: This bicycle rear derailleur is made of high-hardness aluminum alloy, which is sturdy and durable, not easy to deform, not easy to damage, and the speed change is more stable. 4. Precise adjustment: High-hardness aluminum alloy body adjustment, more precise adjustment. Fine-tuning can be performed in multiple positions to ensure accurate speed change performance. Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.