Univen Carbon Pre Filter Element Captures Odors and Large Particles Disposable - Requires No Cleaning Replaces Vornado MD1-0023 Fits Vornado Air Purifier Models AC300, AC350, AC500 and AC550 Univen carbon pre filter element. Captures odors and large particles prolonging the life of the HEPA filters. Univen disposable Carbon Filters require no cleaning. Made to replace Vornado MD1-0023. Fits Vornado air purifier models AC300, AC350, AC500 and AC550. Measures 11.8"(30cm) x 10.2"(26mm). Another quality part by Univen.