The BC-219 roof bike carrier mounts to your vehicle's existing crossbars, allowing you to safely carry your bicycle on your roof. The bike rack's front housing attaches to the front cross bar by installing two mounting plates and four knobs onto the front four screws. Two screws slide along the bottom of the wheel tray to adjust to your back roof bar, and secure in place with a mounting plate and two knobs. For proper stability, the two roof bars should be at least 15.75" apart. This roof bike rack holds your bike's front forks in place with a 9mm skewer that secures with a nut and lever system. The back wheel fits into an adjustable wheel holder and is held in place with thick rubber straps. The BC-219 roof bike carrier includes a 1 year warranty.