Motorola "STX" Series Earpiece Accessory Model NTN4742A.

The STX Earpiece Accessory is an additional item for all STX radios specifically designed for high noise environments. It consists of an earpiece, cable, and connector housing which mounts to the radio side connector.

With the unit attached to the radio, the internal radio speaker is muted and audio is enabled through the earpiece, however the radio microphone and Push-To-Talk (PTT) switch remain operational.