Paper Air Filters
The pleated paper, or dry, air filter is the most popular type but must be replaced when dirty. On carburetor-equipped engines, it consists of an accordion-pleated paper element within a circular rubber or foam structure. It looks like a big donut that would let air enter through the sides, but not the top or bottom.
ROUND AIR FILTER
Courtesy of Car Care CouncilEngines with port fuel injection usually have the paper air filter located inside a box-like air cleaner housing. The housing cover is secured with snaps or screws. The filter element is a solid rectangle in shape. Some filter elements are impregnated with charcoal to trap moisture as well. If so, replacement filters must be of the same type.
RECTANGULAR AIR FILTER