The M-2 mining probe droid was a type of probe droid used in mining. The Subtext Mining company were known to supply them.
One unit of this sort was on Bal'demnic in 67 BBY, where Darth Tenebrous and his apprentice, Darth Plagueis, used it to investigate a cortosis lode. Subtext Mining sabotaged their own droid, hoping to kill the Sith Lords—rather than seeking out the precious metal they desired, the probe instead searched for the flammable gas lethane, and succeeded. The resulting explosion tore through the caverns, and though both Sith escaped, Plagueis used the opportunity to kill Tenebrous.