Product review (4 stars): Now I know to replace.
The humidifier filters did fit into my furnace humidifier.  I have not used them since it is summer.  However, one is installed and ready.  I kept the old one until I knew they matched.  I am another that did not know they were to be replaced not cleaned.  I cleaned the old one until it started rusting.  Then, started looking and was pleased to find these.  Happy.