http://www.flowcine.com/black-and-accessories/98-the-black-arm.html "Mounting options Mounting the Black arm is as simple as clamping it on to a standard 48-52mm speed rail."
Google "speed rail", but if you don't already know what speed rail is you should think about hiring a good key grip. Car mounts are not anything to mess around with as they can be quite dangerous if not done properly.