Respironics - Millennium - Oxygen - Concentrator - 3 - Piece - Filter - Kit
Respironics Millennium oxygen concentrator uses this three-piece filter kit to fit all models from 3-10 Liters per minute.
For best performance and highest purity these filters should be replaced every 300 to 500 hours depending on how clean the area is where they operate. If your concentrator looks like the image below this filter kit is what you need. You may have purchased it as a refurbished unit from Extreme Oxygen, Ultimate Oxygen, Available Oxygen, Oxygen Machinery Group, Salt City Glass or others.