Tap size for exhaust manifold mount holes

[girraf]

Straightforward question. What size tap do I need to run through the holes in the block to mount up my new Barr manifolds? Standard V-8 motor. Bolts look like the may be 5/16”?

 

[kenny nunez]

3/8” 16 theads per inch. Never Seize is always helpful if you ever have to remove the manifolds.

 

[Scott Danforth]

I actually use Maalox on exhaust bolts, dip it, let it dry a bit, then install. 20 years later the bolts will still come out. anti-seize is ok, unless the head is aluminum. on aluminum heads it becomes ever-seized