I want to screw in 2 barb fittings into my manifold for a PCV setup and I am not sure what size threads would be in the manifold.
Probably BSP or NPT. (Because all my taps are UNC/UNF/Metric)
Does anyone know for sure what thread size they would be? I am hoping to get the old plugs out without damaging the manifold but they have been glued in really well. So I can't measure the size and TPI.
This is the type of manifold http://www.redlineauto.com.au/p-138-red ... XA7DmAw8aI
Here is a photo showing the 2 plugs in there at the moment. Cheers Brad

5/8-18 UNF.
it's around 1mm smaller than a 3/8 BSP. I put the 3/8 BSP barb or nipple or hex plug in the lathe, turn it down to 5/8" and run a 5/8 UNF die nut down it. The BSP thread was 19tpi, the UNF thread cleans it up fine.
I tend to use a solid brass 3/8 BSP hex plug, make it 5/8 UNF then tap it 1/4 BSP and use 1/4 brass fittings.

The other way to fix it is run a 3/8 BSP tap into the manifold, but I prefer leaving the threads in it original.

[edit] some newer Redline 3005 manifolds are tapped 1/4 BSP.
Here's one I piped up recently, for a servo and a Toyota PCV valve.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks Doc.
I guess the first thing is to get the plugs out and see what damage that causes. I will probably just go for the easy way out with a BSP tap. I have a few of the 3/8BSP barbs that go into airtools etc.

All done. They were 1/4 BSP so I just used a couple of air tool fittings.

Looks good.
Some people say you should not run any balance pipe on a Weber manifold, and just hook the pcv valve to one port. But I find on a road car, the idle is better with one fitted. As with a PCV valve on 1 port only, you need to run that side richer at idle.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Exactly why I went with the 2 ports.
Its slowly getting there. It used to have a 5L oil bottle as a catch can. Now it has a charcoal canister for a more standard look. The hoses I used were left over from my sprinkler system and hold water pressure fine.