Connect your Baofeng UV-3R with a 4-pole 3.5mm plug to the TNC with this cable. This is a 6" cable with a 3.5mm 4-pole connector for the radio and a 3.5mm 4-pole connector for the TNC.
Please note the connector on the cable pictured. There are a couple variants of the UV-3R. Some use this custom cable with a single 3.5mm 4-pole TRRS connector. Others use a standard Kenwood style connector. Please choose your cable carefully.