The Chrome Plated Aluminum STANDARD double socket arm has a socket at either end to allow a 1" diameter ball accessories to be connected. Overall Length: 3.6875"Socket-To-Socket Length: 2.875" The ""U"" in the part number reflects product packaged in poly bag. For additional specifications, see components and drawings tabs.Powder Coated Marine Grade AluminumChrome Finish1 Inch Rubber Ball