These two wheel forks (or carriers) were cobbled together using parts from Yakima and from Thule, and have worked very well for me. They have clamps to fit on a round crossbar. Each fork carries one wheel upright on one crossbar. They are useful if you carry a bike with its rear wheel held in a tray on one crossbar, and the bike's empty fork clamped to the other crossbar with a skewer. Yakima has a product for the same purpose, priced at $99 for each fork.