Package Included: 4x Rubber Training Wheels (2x Black Color +2x Red Color) Made of high quality plastic and rubber, which is anti-slip, wear resistant, and help kids to ride a bike without fear. Light weight and Easy to install. Sizes: 11x11 CM / 4.33x4.33 INCH Suitable for Children's Bicycles of 16 18 20 22 24 Inches The wheel axle hole is 9.2mm/3/8inch.