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Discussion Starter #1
I managed to twist one of the cooler line fittings in half on my transmission and can’t figure out what size it is.


TH-350. Not original to my car so I’m not certain what year it was manufactured or what it was first installed in. It does have the standard Chevrolet bellhousing. The cooler lines themselves are 5/16” with flare fittings.

The fittings have straight threads and 18 threads per inch with a flat sealing washer that mates against the case. The threaded portion looks to be about 1/2” in diameter, but a 1/2” wrench will not fit over the threads. A 9/16” wrench just rattles around on it.

If I can identify the threads that go into the transmission case I will likely just replace these fittings with a -6 AN adapter and graft new -6 lines onto my 5/16” cooler lines.

Help?
 

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Premium Member
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Discussion Starter #3
1/4 inch nps-18 threads per inch to inverted flare female Is what you broke. 1/4 inch male to 6an male if you want to go to an fittings.

Summit has a bunch of different brands available. https://www.summitracing.com/parts/ear-940006erl?rrec=true

Yours has the metal crush washer. So stick with that type over the o ring type usually found on the Turbo 400 trans.
Thank you. I had to resort to Amazon, as I want to get it back together and Summit won’t ship until the 28th.

On a related note, I’ve never been able to figure out thread sizes past the standard USS and SAE. Those make sense. But how is it that a 1/4 NPT or NPS fitting is slightly larger that 1/2” in diameter? I can only guess they are talking about threaded pipe with an inside diameter of 1/4”?

Those and tubing fitting sizes make my head spin.
 

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I have plenty of used stock fittings if you still need one....cost of postage only charge
 

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Discussion Starter #5
I have plenty of used stock fittings if you still need one....cost of postage only charge
Thank you for your offer. I ended up buying some fittings to adapt -6AN hoses to the case. I honestly don’t think this TH350 is going to last very long and it dawned on me that 1) lining up and tightening the stock inverted flare fittings is a nuisance, and 2) once I have the AN fittings on my stock lines I can easily make hoses to fit whatever transmission I may replace it with and not have to wrestle the hard lines into submission.

Tom.
 

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Thank you. I had to resort to Amazon, as I want to get it back together and Summit won’t ship until the 28th.

On a related note, I’ve never been able to figure out thread sizes past the standard USS and SAE. Those make sense. But how is it that a 1/4 NPT or NPS fitting is slightly larger that 1/2” in diameter? I can only guess they are talking about threaded pipe with an inside diameter of 1/4”?

Those and tubing fitting sizes make my head spin.
Yes, national pipe size names are ID but the sizes called are nominal because through the years better metal allowed for thinner walled pipe but taps and dies were already set for the pipe OD so now pipe does not measure either ID or OD what it's called.

Straight pipe threads are used on some things such as electrical fixtures and fittings and like the above pictured fittings that use gaskets rather than tapered threads to make the seal.

One thing that makes it more confusing is that some fittings with straight threads are almost the same size as NPT sizes are are hard to tell apart.

Tubing makes sense because it's measured by the O D
 

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Discussion Starter #7
Yes, national pipe size names are ID but the sizes called are nominal because through the years better metal allowed for thinner walled pipe but taps and dies were already set for the pipe OD so now pipe does not measure either ID or OD what it's called.

Straight pipe threads are used on some things such as electrical fixtures and fittings and like the above pictured fittings that use gaskets rather than tapered threads to make the seal.

One thing that makes it more confusing is that some fittings with straight threads are almost the same size as NPT sizes are are hard to tell apart.

Tubing makes sense because it's measured by the O D

Tubing DOES make sense until you need flare fittings for it. It seems that those fittings are measured just like nuts & bolts. So I have some 1/2” inverted flare fittings coming to fit where my 5/16” tubing goes.

Ugh....
 

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Discussion Starter #9
The hole in inverted flare fittings is the clue, they fit the tubing snug.
Yeah, but for this job I needed an adapter fitting to go into my radiator so I could add an auxiliary cooler off of that port. So no 5/16” line. Just the fitting. Good news is that I’m just smart enough to know what I don’t know and Team Chevelle can usually get me a quick answer!
 
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