Air injection hole specs?

[racydave]

Friends car, 1800 head on a 2L. The air rail has been removed and I need some bolts to plug the 4 holes. What size are these? ( please and thanks )

[lanciahf]

1800 head uses 12mmx1.25 threads. You can use four old wheel bolts. Cut off the heads and slot the stud with a hacksaw. Then you can use a screw driver to screw them in. Use locktite to lock the threads.