The Rhino-Rack Load Holder is designed so that you can secure your load in position so it doesn't slide in transit possibly damaging other items you have mounted to your roof racks. The RLH1 is designed to fit Rhino-Rack's Heavy Duty Bars.
 
Features:
Quick release over centre cam for a quick and easy adjustment
Allows the profile to be minimised to 130mm
Sold in a pair
It's a great little accessory that is recommended for use if carrying multiple elongated items.