Usage Tips:Feature:1. Made of good quality aluminum alloy, durable and sturdy, equipped with accurate welding technology, can bear heavy duty.2. Equipped with a connect pin, can hardly get opened, also once you install them up, they will not easily fall off, which can ensure your baby's safety.3. Easy to install, only you need to do is fix them with a screw nut on the bike, and insert the trailer attachment, put the pin on.4. A bike trailer coupler is a part that you can connect your trailer to your bike allowing you to transport your little ones in safety and comfort.5. This bike trailer coupler hitch attachment is suitable for baby trailers and most bicycles.Specification:Item Type: Bike Trailer CouplerMaterial: Aluminum AlloyBicycle Fixing Hole of the Rear Axle Diameter: Approx. 11mm / 0.4inTrailer Fixed Hole Diameter: Approx. 7mm / 0.3inRecessed Area Screw Nut Fixed in Diameter: Approx. 21mm / 0.8inBase Plate Length: Approx. 55mm / 2.2inApplication: For baby trailers and most bicycles.Package List:1 x Connect Pin1 x CouplerNote:1. Please allow 12mm/ 0.040.08in error due to manual measurement.2. Please measure your trailer coupler and bike mount size before order this adapter.