Articulated Arm, "B" Size Balls, Short Length Metal Arm, Plastic Base Plates
Note: I prefer the plastic arms to the metal ones because they are a little lighter and very rugged.  The plastic bases are also very rugged. The metal bases work best with Nimbus Cradles.
Articulated Arm, Length: 4.1 inches (104 mm), aluminum arm, 2 plastic base plates with large 1" (25.4 mm) balls, weight: 4.2 oz (119 g), Diamond shaped mounting plates are 1.25" (31.8 mm) x 2.5" (63.5 mm).  Mounting hardware not included. This kit contains a RAM-B-201U-A arm and 2 RAP-B-238U base plates.