Arkon SPRM5780 Robust Series 8 inch Aluminum Mount Shaft Arm - 57mm (2.25 inch) Ball Compatible (sku 56043)Use with Arkon 57mm (2. 25 inch) adapters and holders (sold separately) to create a custom solution Aluminum shaft measures 8 inches (127mm) tall Compatible with 57mm (2. 25 inch) Arkon Robust Mount Series or Ram Mounts Size D The SPRM5780 Robust Mount Shaft is part of Arkons Robust Mount Series and can be used with 57mm (2. 25 inch) compatible adapters and holders, including those from Arkon as well as Ram Mounts and other third party manufacturers.