This Numatic Permatex primary filter is suitable for the larger commercial/industrial vacuum cleaners with a 356mm drum. A primary filter protects the motor of the vacuum from the ingress of fine dust. The design and makeup of the Permatex filters provide a filtration level of 99% at 0.5 microns when used with the Numatic HepaFlo dust bags. The Permatex filter is both durable and washable (by hand). Unlike standard Tritex filters, the Permatex is reusable offering a good return on the original investment.