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. Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.