Exhaust manifold bolt thread size?

[LewG]

Hello,
can someone tell me what tap I'll need for my manifold bolt holes? Had to drill a couple of seized bolts out and am now looking to retap to the original size.
Cheers

[Richard 858]

3/8" unc, I'll check the exact pitch after tea, in about an hour.

[LewG]

Superb thankyou, I have checked with my metric gauges and it appears to be 1.5?

[Richard 858]

Just to confirm 3/8"NC16. Definitely an imperial thread NOT metric.

[jojackson4]

Don't put a metric one in

[LewG]

Grand job cheers, that's the tap I've ordered. Had to drill both out on the last cylinder RH bank. Got it dead central yet even with a screw extractor both refused to budge!