1. This bicycle derailleur hanger adapter is made of aluminum alloy, offering good durability and stability to provide reliable support for your cycling experience. 2. It comes in two specifications: the long version L41 and the short version L23. Different specifications can meet different usage needs. Whether it's a road bike or a mountain bike, you can find a suitable adapter. The long version L41 can achieve a longer derailleur hanger extension, providing more expansion space for the bicycle, which is suitable for cycling enthusiasts with high requirements for frame space. The short version L23 is more compact, meeting the needs of those who don't have high space requirements but need precise adaptation. 3. This derailleur hanger adapter can be used as an extension seat for mountain bikes and can also be adapted to rear derailleurs and cassettes, effectively improving the performance of the bicycle. It can make the operation of the rear derailleur smoother and shifting more accurate, allowing you to easily handle various road conditions while cycling. 4. Whether you're speeding on flat roads or navigating through rugged mountains, this bicycle derailleur hanger adapter will be a good cycling companion, adding more functions and practicality to your bicycle.