Feature: 1. Oiling Chain: Flywheel cooperates with sponge ring to oil chain. Keep chain tight, away from frame and paint. 2. Magnetic Storage: Small size design, convenient storage, adsorption of iron tool wall, and small steel screws. 3. Simple Rolling Ruler: Can be used as an emergency measuring tool when going out. 15cm total length, record the number of rolling circles, and you can calculate the corresponding length. 4. Use Purpose: To prevent your chain from getting tangled during transportation or when cleaning the chain, and to prevent frame from scratching. 5. Chain Cleaning: Replace the rear wheel on the bicycle for cleaning, transportation and maintenance, and fix the chain in place. Suitable for barrel shaft with diameter of 12mm/0.5in. Specification: Item Type: Bicycle Mountain Road Chain Retainer Material: Nylon Color: As Pictures Shown Weight: Approx.54g/1.9oz Style: RL210 Barrel Shaft Version Application: Suitable for Barrel Shaft with Diameter of 12mm/0.5in. Package List: 1 x Flywheel2 x Foam Ring1 x Storage Box