Bike Bicycle Trailer Coupler Attachment A bike trailer coupler is an ideal way to do that. This is the part that you can connect your Schwinn or InStep trailer to your bike. It is called a coupler, it acts like a trailer hitch for your bicycle. With bike trailer attachment, the bike trailers are easy to attach to your bike while allowingyou to transport your little children in safety and comfort. How to know your trailer code? The determine the date of manufacture of the trailer, look for a date code on the trailer's tow bar. It is usually on a sticker.