[Universal Diameter and Available Size] Still bothered by the fact that some bike training wheels can only fit one or two sizes of bicycles? Our training wheels with bracket attached feature 5 various holes to fit bicycles with wheel sizes: 12, 14, 16, 18, and 20 inches. The round design and attractive appearance complement each other, offering a fun look that children enjoy. (Note: Not compatible with variable-speed bicycles) [Thickened Wheel with Quality PU Material] Designed for durability and quiet performance, these training wheels are made of high-quality PU material that provides shock absorption. The wheel thickness measures 2.5 cm, which is 0.5 cm thicker than standard wheels, helping to reduce bumps for a smoother, more comfortable ride with less effort. [Double Bearing and Larger Washer] Equipped with double high-carbon steel bearings, these training wheels deliver smooth, quiet operation and extended lifespan. The washer has been enlarged to fully cover the bearing, helping prevent loosening or detachment during use. This added security supports safe riding and confidence as your child learns. [Thicker Bracket, Stronger and More Durable] To address common issues like bending or breaking, the bracket is designed with a 3 mm thickness—20% thicker than standard brackets—providing enhanced support and resistance to deformation. This durable construction ensures reliable performance as your child gains riding skills. [Easy Installation] Comes with a wrench for simple setup. The locking brace helps secure the bracket firmly to the bicycle frame. For optimal performance, adjust the training wheels so they are approximately 5 mm above the ground when the bike is upright. This allows room for balance development while providing stability. Color: Blue Material: Plastic Package Contents: 2 x Wheels 1 x Wrench 2 x Screws and Nuts 2 x Cushions Note: Light and display differences may cause slight color variations between the product and the image. Measurement may vary by +/- 1-3 cm.