Safety Assist Function: Child safety is most important. Our product weighs 1.1 kg. Sturdy training wheels help children maintain balance and provide greater safety and stability. Sturdy and durable: the upgraded version of thick high-strength 3MM carbon steel material, a stable ride without deformation. The wheels are made of environmentally friendly PVC, non-slip, wear-resistant, durable and low noise. Easy to install: use a wrench to install the drive wheel on the rear wheel of the bike to adjust the distance between the vertical support and the ground. If you have any questions, please contact us, our professional customer service will answer all your questions. General size: Our training wheels are suitable for 18-22 inch bicycles, meeting the needs of children learning to ride at different times and providing them with secure support. Compatibility: Our products are suitable for children's bikes and variable speed bikes. Install our special extension screws on the side of the shifter. After installation, please make the main wheel perpendicular to the ground, and confirm that the auxiliary wheels on both sides have a height of about 0.6-1cm from the ground (installation tools are provided by yourself).