|Out of universe information|
- "P4M-399. It's a — it's a tiny little planet right on the very outskirts of our galaxy"
- —Bill Lee
P4M-399 was a planet designated by the Tau'ri in the Milky Way galaxy. 399 is a small planet found on the outskirts of the Milky Way. A science team from Stargate Command was dispatched to this planet to set up and transmit a subspace message to the starship Daedalus, traveling in-between the Pegasus galaxy and the Milky Way. (SGA: "Critical Mass")