The Zenmuse H3-3D Mounting Adapter for Original Phantom from DJI is a bundle that includes a special mount and extended landing gear allowing the GCU-equipped version of the Zenmuse H3-3D to be used with the original Phantom.
Note: Unlike the Phantom 2, the original Phantom does not have an integrated GCU (gimbal control unit) therefore it is important to ensure the version of the Zenmuse H3-3D you use is one that includes the GCU.