Wheels diameter: approx. 11 cm/4.33 inch. Universal training wheels fits for 12/ 14/ 16/ 18/ 20 inch children's bicycles. These bicycle training wheels are made of high quality plastic and rubber which it is anti-slip, wear resistant, providing stability and help children to ride a bike without fear. Light weight and noiseless.Besides, they roll smoothly.Note: This product can only support children under 80 pounds. They can provide the necessary security and stability which it needs in the first road tests on the bike. Gives your child the best start to gain their balance and confidence on two wheels. Easy to install, just install the training wheels with brackets.(with mounting bracket)Tips: This product does not apply to certain models of HUFFY bicycles.