Usage Tips:1. materials The bicycle trailer hitch attachment made of steel with black enamel coating, made of durable iron material, strong and durable, corrosion-resistant, difficult to damage.^2. Appropriate size The diameter of the rear axle mounting hole of the bicycle: 11mm Diameter of the mounting hole of the connecting trailer: 7mm The diameter of the recessed portion where the shaft nut is screwed: 21mm Base plate length: 55mm^3. Ensure safety Every bicycle trailer is equipped with a connecting pin. The pens can hardly be opened. Even once you have them installed, they do not fall off easily and can keep your baby safe.^4. Easy to Install First, attach the tow bar of your bike trailer to your bike with a screw nut. Then insert the trailer attachment; Finally put on the pen; The connection is ready, bring you a lot of convenience.^5. Wide application You can use it to pull strollers and pet strollers, and bring children and pets when you ride a bike in the park, which is very convenient and safe.^