Package Contains --- Training wheels included 2 x wheels, 2 x vertical bracket for 12-20 inches bike, 2 x limit spacer, 2 x bolt, 2 x nut, 2 x washer, 1 wrench. The wheel diameter is about 4.3 inches, and the bracket is 6.9 x 1.2 inches, providing additional stability and safety. High-Quality Material --- Our bike training wheels are made of high quality alloy steel and rubber with sturdy metal supports that are slip and wear resistant. Improve your child's safety and confidence without worrying about the backrest of the saddle. Heavy Duty & Flash Mute --- Training wheels are built with a structural reinforcement design that makes them sturdy for a longer product life. This set of heavy duty rear wheel stabilizers assists young learners to ride bicycle until they have developed a usable sense of balance on the bicycle. Improve your child's safety and confidence. Light weight, flashing silent wheel to keep you away from the noise. Adjustable Size --- The training wheels are suitable for 12 to 20 inch bicycles and can be adjusted according to the child's bike riding skills and level. The support wheels are individually strong and adjustable, providing the security and stability needed for bicycling. Easy to Install --- All mounting hardware and installation instructions are included inside and you will have more options to adjust the height. The training wheels can be used for long periods of time and are perfect for kids on bikes.