RAM A size, 9/16", holds up to 1 lb. Mounts Australia offers a wide range of RAM mounts.
RAM 2.43" x 1.31" Diamond Ball Base with 0.56" Ball (RAM-A-238U)
RAM Double Socket Arm for 0.56" Balls (RAM-A-201U)
RAM 0.56" Double Ball Adapter (RAM-A-230U)
RAM Long Double Socket Arm and 2 Diamond Bases with AMPs hole pattern Ball Mount (RAM-A-101U-B)
RAM Long Length Double Socket Arm for 0.56" Balls (RAM-A-201U-B)
RAM 0.56" Ball with 1/4-20 Male Threaded Post for Cameras (RAM-A-237U)
RAM 0.56" Ball with 1/4-20 Female Threaded (RAM-A-336U)