Bubbler Humidifier for Oxygen Concentrator by Salter Labs.  Features Universal fitting to fit most Oxygen Concentrators.  Oxygen RX Required for Purchase.

TIPs:

1. Fill only about half way full.(if you fill it to full, the oxygen will not come through into the tubing)
2. Use DISTILLED WATER ONLY!(if you don't, it will clog the filter)
3. Be careful not to cross-thread (mis-align when securing the lid or cap to the concentrator)
4. Recommended for people who experience dryness during oxygen use.