The Aprilaire 4004 Humidifier Inline Strainer replacement is used in all Aprilaire humidifier models EXCEPT:
Strainer filter fits in to the inlet fitting of the water solenoid valve of your Aprilaire humidifier which allows water to enter your humidifier. It is designed to keep debris from entering the solenoid valve and clogging it. The Aprilaire 4004 humidifier strainer component should be cleaned periodically and changed as needed.
The Aprilaire 4004 specifications:
This is a genuine factory replacement Aprilaire 4004 In-line Strainer also known as the Aprilaire 4004 Strainer and April Air 4004 Strainer.