About this product: Size: This product is used for most products, the diameter is larger than you see, but you can adjust it with a tool to make it very stable. Diameter of the hole in the hitch where the trailer attaches: 6.8 mm. Diameter of the recessed area where the axle nut screws on: 21mm. Diameter of the hole in the hitch where the trailer attaches: 6.8 mm. Base plate length: 55 mm. Portable Design: Bike trailer with vertical and horizontal holes on the trailer coupler, so whichever hitch hole your trailer has, vertical or horizontal, it works great for you. Multi-compatibility: Made of heavy-duty steel with a welded hitch arm at an approximate 45 degree angle for an ideal mounting position for many types of bike trailers. Stable: very practical to use. Just attach a hitch to all the bikes in your house and you're ready to use the trailer with all the bikes. Once you tighten the wheel well. It will stay securely in place. Family Fun: With an additional trailer, mom and dad's bikes can be used to tow the kids' trailer, your kids will love the bike.