Permatron hospital-grade prefilter for Honeywell F52F1048, single-cell model. Uses one prefilter. Verify prefilter dimensions; F52 models were manufactured with different prefilter sizes. This 208536 prefilter measures 21-3/4 x 12-5/8 x 5/16 inch. Permatron, premiere prefilter manufacturer, designed this prefilter to exact Honeywell specs. Metal mesh consists of five layers of slit and expanded aluminum of differing densities. The frame is upgraded to stainless steel.