This is an Eagle Tree Systems Male RCA to Servo Connector Adapter. This adapter is used with the OSD Pro Expander. Most FPV systems are compatible with the OSD Pro System and are capable of providing real time data simultaneously with your video feed. The only requirement is that there needs to be a cable running between your video camera and video transmitter to run through the OSD Pro Expander, which is how the expander gets the data overlaid onto the video feed. The OSD Pro Expander uses servo connectors, so if your cable uses RCA plugs to connect the video camera and video transmitter, this helpful RCA to Servo Connector Adaptor cables (product code CAB-RCA-SRV) can help you do that.
NOTE: Most applications will require two - one for line in and one for line out of the OSD Pro Expander. Can also be used for audio if your video transmitter's audio uses RCA plugs.