For SINGLE SPEED BIKES: Features 5 1/2" diameter plated steel wheels with rubber tires. Intended for use by riders weighing up to 100 pounds. | The new frame adapters enable this wheel set to be mounted on bicycles with .75 and 1.00-inch rear frame tubes | The training wheels can also be mounted onto bicycles with 1.25-inch rear frame tubes when the frame adapters are not used. | Easy to install. To fit properly 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, not designed for multi-speed bicycles.