RAM® 4" Square Post Clamp Mount with Round AMPS Plate

• 2.5" round plate connects to RAM® device holders containing the universal AMPS hole pattern
• Includes 4" clamping base for posts and a medium length, C size RAM® double socket arm; ball and socket technology allows for near-infinite adjustability
• Made of powder-coated, marine-grade aluminum for durability and reliability in the most demanding environments
• Backed by a lifetime warranty

More info here.