Our 742 training wheels feature three slots on the brace arm allowing this wheel set to mount on most single speed bicycles with 16 to 26 inches wheels. The brace arms are designed to fit rear frames tubes up to .75 inches in diameter. This model is intended for use by riders weighing up to 125 pounds. FEATURES: In order for Wald training wheels to fit your bicycle, there must be at least 3/8? of axle outside the axle nut on both sides of the rear wheel. Wald training wheels are designed exclusively for single speed bicycles. They are not designed for multi-speed bicycles. Wald training wheels are designed to be training aids used for a temporary period of time. If the rider has special needs or exceeds the designated weight limits, we cannot recommend our products for their use.