This bike wheel is mainly used to protect the center bolt derailleur of the bicycle, so that the pulley runs on smooth ball bearings, thereby effectively extending the service life. Specifications: Material: Aluminum alloy, steel Model: 11T/ 13T (optional) Color: Black/ Colorful/ Red (optional) Size: 4.4*4.4cm/ 1.7*1.7in Weight: 11.4g/ 0.4oz Package list: 1 * wheel