this is an intake for the predator 212 engine i bought from harbor freight. the end has a 40mm O.D. to clamp on universal air filterstake the stock air box off and bolt this one on in its place. i bought this filter (http://www.amazon.com/gp/product/B00AM6JXE6?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00) that has a 39mm id.