[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 kids enjoy. (Note: Not compatible with variable-speed bicycles)[Thickened Wheel with Quality PU Material] Designed for quiet and durable performance, these training wheels are made from high-quality PU material, providing excellent wear resistance and shock absorption. The wheel thickness measures 2.5 cm, which is 0.5 cm thicker than standard wheels, helping reduce bumps and ensuring a smoother, more comfortable ride with less effort.[Double Bearing and Larger Washer] Equipped with dual high-carbon steel bearings, these training wheels have been tested for smooth, quiet operation and extended durability. The washer has been enlarged to fully cover the bearing, reducing the risk of loosening or detachment during use. This added security helps prevent unexpected falls, promoting safer riding and confidence building.[Thicker Bracket, Stronger and More Durable] Addressing common issues of bending or breakage, our training wheel bracket is 3 mm thick—20% thicker than standard brackets—providing enhanced support and resistance to deformation. This robust construction ensures long-term reliability as your child learns to ride.[Easy Installation] Comes with a wrench for simple setup. The locking brace helps secure the bracket firmly to the bicycle frame. Installation is straightforward and user-friendly. For optimal performance, we recommend adjusting the training wheel so it is approximately 5 mm above the ground when the bike is upright. This allows your child to gradually develop balance while riding.Color: Blue Material: Plastic Package Contents: 2 x Wheels 1 x Wrench 2 x Screws and Nuts 2 x Cushions Only the above package content is included; other items are not part of this package. Note: Lighting and display differences may cause slight variations in color between the image and the actual item. Measurement may vary by +/- 1-3 cm.