Material: The bike trailer hitch attachment is made of steel with black enamel coating, made of heavy-duty iron material, strong and durable, anti-corrosion, difficult to damage. Size: 90° bike trailer hitch. Fits QR axles and solid axles up to 12mm (OD=0.48"). Each bike hitch is equipped with a connecting pin, the pins can hardly be opened even once you installed it, they are not easy to fall off and can ensure your baby’s safety. The package includes 2 packs of bicycle trailer hitch kits. With this additional trailer hitch attachment, both mom and dad’s bikes can be connected to the child trailers.