9S sprocket adopts quenching and tempering hardening technology, which makes it wear-resistant and has long service life And the colorful electroplating on the surface is cool and shows personality It is the hollow design that makes this sprocket have the effective speed change Lost gear design makes the shifting smoother This sprocket is made of high quality chrome-molybdenum steel material that is wear-resistant and durable This colorful sprocket is suitable for cycling Specifications: Item Name: Sprocket Material: Chromium Molybdenum Steel Speed: 9 Speed Number of Teeth: 11T-28T Gear Ratio: 11-12-13-14-15-17-19-21-23-25-28T Features: Colorful, 28T Electroplating, Hollow Size: 13cm x 13cm x 5cm/5.12" x 5.12" x 1.97" (approx.) Package included: 1 x Sprocket 1 x English and Chinese User Manual