What thread size for 69 A.I.R. Ports in exhaust manifold?

[Michael L.]

Guys,

i want to run a tap down the threads of the A.I.R. ports in my 69 sb exhaust manifold but I don't want to guesstimate the thread size only to discover that I've ruined my manifolds by using the wrong size tap. Does anyone know the size of the thread this is?

Mike

[Dick W.]

Re: What thread size for 69 A.I.R. Ports in exhaust manifold?

Believe it is 3/8" tube 9/16X18 thread

[Michael L.]

Re: What thread size for 69 A.I.R. Ports in exhaust manifold?

Thanks Dick. So it isn't some form of pipe thread or something? Just a straight forward 9/16X18?

[Richard K.]

Re: What thread size for 69 A.I.R. Ports in exhaust manifold?

Just measured an NOS A.I.R. manifold tree that is hanging on my garage wall for install on my '69 350 later on. 9/16 x 18 tpi

[Dick W.]

Re: What thread size for 69 A.I.R. Ports in exhaust manifold?

Straight 9/16X18. Tubing thread has no taper like IPT

[Mark D.]

Re: What thread size for 69 A.I.R. Ports in exhaust manifold?

The N. Wilkesboro farmer has reappeared.

[Michael L.]

Re: What thread size for 69 A.I.R. Ports in exhaust manifold?

Just ran the threads on the exhaust maifolds A.I.R. ports. For future reference, at least for my 69 sb 350/350, the thread size is actually 1/2X20. No way 9/16X18 tap fits. 1/2X20 fit perfectly.