The BigStack's narrow profile takes up the least amount of rooftop space and carries up to four boats on their sides. It's padded to protect your boat and vehicle, and the steel-reinforced arms fold down when not in use. Four-boat capacity in a small package. SteelCore construction utilizes a steel substrate encased in durable foam padding. Folds down flat when not in use for the ultimate in rooftop clearance. Hullguard pads protect andkeep your boat looking brand new. Locks to crossbar with SKS system