Features: The high performances designs of folding bike single speed flywheel provide fast cycling speed while saving effort. Mountain bike single speed flywheel have smooth turn action no much noise. Make of aluminum alloys and stainless steels, strong, Rusts resistant and wear resistant. It have high accuracy thread machining to ensures a tight connection with the bike wheel andsilky running. It can directly replaces old and broken accessories, ensuring the normal of your bike. Specifications: Materials: Aluminum alloys and stainless steels Number of teeth: 12T or 13T or 14T or 15T or 16T or 17T or 18T or 19T or 20T or 21T or 22T Size: as shown in the picture Package Includes: 1set Single Speed Flywheel(Random color) 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.