Axial Air Filters have higher efficiency than conventional air filters. Changes have been made on its structure such as the addition of cover caps in different forms, eccentric caps with adjustment notches, secondary or safety filters for two-stage filtration, input systems with vanes in the housing or diffusers with fins in the primary filter. Filtration in heavy diesel vehicles has cyclone shells, oblique deflectors in the intake compartment with dust compartments, dust extractors, cyclones with dynamic turbine, among others. In two-stage filtration, some filters were built on a flange with screws secured to the flange of the secondary filter; these screws were in the housing or in the filter.