Honeywell 203369 Pre-Filter Compatible with models F300E1035 and F300A2025 Compatible with models F50F1065 and F58F1000 Compatible with models F300A2012 and F300B2012 Compatible with models F50F1040 and F50F1057 Dimensions: 20 x 12.5 x .34 Inches, Two prefilters needed for Honeywell 20 x 25 air cleaner cells. Only one prefilter is needed for the 20 x 12.5 air cleaner cells