The AP38CM1420 circular metal 38mm ball to 1/4”-20 camera bolt adapter is compatible with 38mm (1.5 inch) mounts and pedestals, including those from Arkon or RAM Mounts (Size B). (Mounts, holders, and devices sold separately.) The 1/4”-20 camera bolt is compatible with cameras and other devices having a 1/4”-20 mounting pattern. The adapter's round plate design is a great alternative for locations or devices where a square adapter won't work.