The bag has a spring-supported ABS plastic clip on the front, which latches upward onto the forward-most lateral bar of the Topeak rack. When it clips in place, it's connected/held down solidly. The MTX bags do not have any sort of clips or straps for non-Topeak racks, and therein lies the rub: Buying the MTX trunk bags without purchasing the MTX rack to go with them is not a good idea. Thanks to the plastic rail which runs along the bottom of the bags, they don't seat as well onto other rack types.