The air pump passages in the heads use an expansion plug that is readily available from your local auto parts store. Sorry, I don't have the part number at the top of my head and keep forgetting to grab it when I am at the shop. Next time I remember I'll bump the thread up with a post that has the part number. I think they are around 43/64" or something like that. Pioneer makes them, etc. There is no need for a screw in plug at this location.