hitch insert fits 2 inch (us)/ 50.8 mm (europe) receiver hitches quick install hitch secures and tightens rack inside of receiver hitch; includes 2 keys arms fold out of the way when not in use and rack tilts back when needed individual tie downs secure and protect bicycles accommodates a wide range of bicycle frame designs ; Included components: Hitch Mounted 4-Bike Carrier with Locking Quick Install Hitch