Features: Adopting waterproof function, it can effectively prevent water and dust from entering the bearing, extending their service life. Crafted from reliable bearing and metal materials, providing stable operation performances and durability. Featurings a square hole, it is tightly connectings to bicycles base, enhancing stability and transmission efficiency. Comes with waterproof screws to enhances the sealing between the center axles and bicycles frame, effectively preventing water intrusions. Suitable for road Bicycles, mountain Bicycles, foldings Bicycles, etc., providing a stable and smooth ridings experience. Specifications: Material: Metal Style: 1/2/4/5/6/3/7/8/9 1 Size: about 68x103mm/2.68x4.05inch 2 size: about 68x107.5mm/2.68x4.23inch 3 size: about 68x110.5mm/2.68x4.35inch 4 size: about 68x113.5mm/2.68x4.47inch 5 size: about 68x116mm/2.68x4.57inch 6 size: about 68x118mm/2.68x4.64inch 7 size: about 68x122.5mm/2.68x4.82inch 8 size: about 68x124.5mm/2.68x4.90inch 9 size: about 68x125.5mm/2.68x4.94inch Package Includes: 1x Square Tapered Bottom Rack 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.