What helps to prevent the chain from falling or subtracting the design of the teeth. CNC handicrafts bring good strength and long time. The hollow design reduces the weight of the bicycle without affecting its strength. It has good toughness and is not easy to deform and rust. The light design makes it not put pressure on your bicycle. It is suitable for bicycles, road bicycles, mountain bicycles. The aluminum alloy material makes it lightweight, safe and stable, and sturdy and durable. The diameter of the 52-Teeth style is 216mm. The diameter of the 56-Teeth style is 231mm. The diameter of the 58-Teeth style is 242mm. It is suitable for bicycles, mountain bicycles, road bicycles, etc. Item Name: Positive negative sprocket material: aluminum alloy: black, red, gold, gold color BCD: 130mm lightweight, stable, security details: 52-diameter: 21.6 cm/8.5 inches (approximately) 56-Teeth style diameter: 23.1 CM /9.09 "(approximately) 58-Teeth type diameter: 24.2cm /9.53" (approximately) Note: Due to the difference in light and screen settings, the color of the project may be slightly different from the picture. Please allow small size differences caused by different manual measurements. Packaging includes: 1 x positive negative chain ring