Occasionally, you’ll come across a connector on the Digi-Key website such as 380-SS-53000-003-ND, which is listed as a 19-position HDMI connector. When this device shows up though, you’ll find 21 pins on it instead. What gives, and what are these extra pins doing on this connector?
The two extra positions on this and some similar connectors are ground pins, located at the front of the contact row. They connect to circuit ground and can be used to assist in signal quality for certain types of HDMI connection.
If left unconnected on a board with no ground trace, the device should work like a normal 19-position HDMI connector, but you won’t benefit from the increased signal quality the extra ground contacts can provide.