The Honeywell 203372 is the correct replacement pre-filter for the following air cleaner models:
The Honeywell 203372 Electronic Pre-Filter - F50A F50E is a replacement washable pre-filter for the Honeywell model F50 and F300 air cleaners. This air cleaner pre-filter measures 20" x 25" and is washable for re-use. This Honeywell pre-filter traps larger contaminants in your air to improve overall indoor air quality.
Honeywell 203372 Electronic Pre-Filter - F50A F50E specifications: