The automobile in question is a '96 Pontiac Trans Am. What do I use to plug the holes left in the manifolds with the air pump goodies removed?

Every post I've read says to use M22 drain plugs. They are WAY too big! The M20 is even a little too large. The 18s look too small and I'm not aware of a 19. Any ideas?

 

Try a 3/4 x 16 plug.

 

The M22 drain plugs are for some headers, not the stock manifolds. I think anaik is right on size.

 

I believe M-22's are for 93-95.. I've herd M-18 for 96-97..

I have 93 header's on my 97 so I'm using M-22's