Air Filter, Race, Open Element (K&N Type), Use with most 2 5/16 air filter adapters.
3.5" x 4" (2-7/16" Opening), Angled

Air Filter, Race, Open Element (K&N Type), Style may vary, Small neck for 22mm Mikunis & Walbros..
Will not fit air filter adapters.
3.5" x 4" (1-5/8" Opening)

Air Filter, Race, Open Element (K&N Type), Use with most 2 5/16 air filter adapters.
3.5" x 6" (2-7/16" Opening),

Genuine K& N,  Use with most air filter adapters, Angled, 3.75" x 4", Large Opening