The Thule Tour Pack 'n Pedal Side Frames are designed to be used with Thule Pack 'n Pedal Panniers. Thule did this in order to simplify usage between the two products, but it makes them incompatible with traditional bags. With these Side Frames, however, the racks will function seamlessly with clip-and-hook style panniers. The Side Frames are constructed from aluminum, and they have a second rail that allows you to place the pannier lower on the frame for safer handling. The Thule Pack 'n Pedal Side Frames are available in one color and one size.