describe About this product: ? Size: This product is suitable for most products, the diameter is larger than what you see, but you can adjust it with tools to make it very stable. Hitch hole diameter at trailer attachment: 6.8 mm. Diameter of the recessed area into which the axle nut is screwed: 21mm. Hitch hole diameter at trailer attachment: 6.8 mm. Bottom plate length: 55mm. PORTABLE DESIGN: The bike trailer comes with vertical and horizontal holes on the trailer connector, so no matter which hitch hole your trailer has, vertical or horizontal, it will fit you perfectly. ? VERSATILE COMPATIBILITY: Made of heavy-duty steel with welded hitch arms at approximately 45-degree angles, ideal mounting position for many types of bike trailers. Stable: Very convenient to use. Just hook up all the bikes in your family and you can use the trailer with them all. Once you have tightened the wheel well. It will stay firmly in place.