Features: Make of Aluminum alloys and stainless steels materials, light in weight and small, easy to installation and use. Function: It can effectively prevent the chain from falling down, and reduce the gear feeling. Floating pulleys and spring designs can fit various size of gear, and prevent chain from skidding out from the cranks. This bike chain tensioner can ensures that the chain reaches great tension, making your pedal operate labor saving. This single speed bike adjuster is suitable for folding bike with 11T or 13T rear derailleurs. Specifications: Materials: Aluminum alloys and stainless steels Color: Black/Redness/Gold Size: as shown in the picture Package Includes: 1set Bicycles Chain Tensioner note: Please allow 1-2cm errors due to manual measurement, make surely that you not mind before order. Due to difference between different monitors, the picture may not reflect the actual color.