The Ortlieb Rack 3 is a proprietary rack designed to accommodate Ortlieb bags with their low-profile QL3/3.1 attachment system. While Ortlieb bags with the QL2.1/2/1 attachment system (and likely other brands of panniers) also fit fine on the Rack 3, its three protrusions fit specifically into the corresponding "hidden" clasps on the back of Ortlieb QL3/3.1 bags. The Rack 3 is suitable for both 26" and 28" bikes and has a load capacity of 66lb (30kg).