Features: With simple design, the tail hook correction tool is easy to use. After locking the tool in the rear variable lift eye, the wheel distance can be marked on the gauge. When turning the gauge to the direction abcd of the wheel, and the position does not exceed 4mm to detect whether there is a difference between the gauge distance and the wheel, then you can immediately get the result. With practical functions, the tail hook correction tool can help solve a multitude of derailleur shifting problems, especially index shifting systems. Made of aluminum alloy material, the tail hook correction tool has a high temperature resistance of 800 degrees Celsius, which is corrosion-resistant, anti-rust and wear-resistant. Bicycle Rear Derailleur Hook Alignment Gauge Tail Hook Corrosion Resistant Correction Tool Bicycle Accessories Specifications: Material:Aluminum Alloy Size:as Picture Shows Note: Please allow 0-1cm error due to manual measurement. Make sure you do not mind before you bid. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you Package includes: 1 x Derailleur Hanger Alignment Tool