Adjustable 1-Bike roof rack carrier transports a single bicycle on an existing vehicle roof rack. The Apex roof bicycle rack is designed to work with existing crossbars up to 3.25in W by 1.625in H with a minimum of 1in from roof to crossbar with an integrated U-bolt attachment system. It s also recommended to the roof cross bars are positioned at least 28in apart for maximum stability. Adjustable clamping arm attaches to bicycle down-tube. Key lockable includes two keys. Safely transport a single bicycle on a vehicle roof easily. Durable steel construction with a sleek glossy black paint finish.