GeneralAire ReservePro 4551 MERV 11 OEM 20X25 filters exactly fits part # 4501. GeneralAire part #4551. Nominal Size: 20" x 25" X 5" Actual Size: 19 5/8" x 24 3/16" x 4 15/16". Efficiency Rating: MERV 11 High-efficiency MERV 11 Media Filter # 4551. Fits GeneralAire GF‐2025, GF‐GAFB2832, GF‐GAFB2843, Mega‐Mac MAC2000, MAC‐L; Lennox BMAC‐20C, MAC‐10, MF1‐20; Source1 S1‐MAC10202505; Totaline P101‐MF20; Trion Air Bear 2000; York S1‐MAC10202505. High-efficiency MERV 11 Media Filter with more surface area for a longer filter life.