they're factory. As you know they're for filter clearance. I ain't 100% sure on this but I'm thinking they did not have or for some reasone did not want to use teacup (short) filters. those adapters are restrictive. If you want the whole scoup from the countries' foremost SB oiling expert (& have an hour to spend perusing the info) go to www.moparchat.com then scroll down to & click on "circle track chat" & then click on Sanborns oiling mods that are in a sticky at the top of the page. FYI alot can be applied to BB's as well. His cooling mods under the oiling mods are just as awesome