Pontiac 9/16 Press In Oil Galley Plug for Front of Block, Set/2

Seals the front end of both main oil galleries. These sit behind the timing cover, one per galley, and this is the factory press-in plug.

The same two holes can be tapped for 3/8" NPT instead, which is a popular insurance step on a high oil pressure build — a press-in plug that works loose can push out and dump oil internally. It is one location with two ways to seal it; the 3/8" NPT plug is not an extra plug somewhere else. Use short-length pipe plugs if you go that route, because a taper threaded in too far will choke the galley.