This filter is an accessory that you can add to any model of Respironics EverFlo. The plastic framework easily clicks into place on the rear of the Oxygen Concentrator. When looking at the rear of the machine, the grates at the top left of the Oxygen Concentrator is where the air enters the unit for cooling the internal components. Over time, lint, dirt, pet hair etc will be pulled inside the machine and can create quite a mess, and eventually will have the potential to cause some issues with your machine. This filter will stop that. Just remove the foam filter every week, rinse it in your sink, let it air dry and replace it. The plastic frame is a good used frame, but the foam filter is always brand new.