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What is the tap/fitting connection size for the low oil pressure sender on a 2L engine block? I plan to check the oil pressure with a mechanical gauge which has a 1/8" npt fitting. I'll need an adaptor to connect it I'm sure.
TIA
Ken
 

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It is 1/8" NPT
 

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My pressure switches have 1/8" NPT tapered thread and the pressure senders are straight metric. The sender requires a little gasket and the switch seals on the threads.
 

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I just removed the plug my mechanic put in the switch hole on my spare engine in the garage. The plug is steel with allen key hole. The plug fit snugly into a brass 1/8 npt female fitting I have and tightens up as an npt thread should. Also the allen key hole is exactly 3/16. 5mm is too big and 4.5mm is too small. The steel plug is definitely 1/8 npt. It would seem crazy for the mechanic to have re-tapped the block from metric to npt just so he could use an npt plug

But it does seem odd for Alfa to have used this thread for this hole, or at all. Is it possible that this hole is npt only in the US? It seems very odd, but it could be true. People outside the US should measure their actual thread and see. The picture above shows that the shaft is the same, but the thread was not measured. It would be interesting to get the thread of those two above.

Is npt not used at all in Europe? I don't know the answer.
 

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My pressure switches have 1/8" NPT tapered thread and the pressure senders are straight metric. The sender requires a little gasket and the switch seals on the threads.
Tapered is correct, Ed but 1/8"?
1/8" is 3,175mm or am I wrong?

People outside the US should measure their actual thread and see. The picture above shows that the shaft is the same, but the thread was not measured. It would be interesting to get the thread of those two above.
Stefano, what do you think shows my picture?? The measured thread .
It's M10x1.
 

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1/8" is 3,175mm or am I wrong?
Not in the case of npt. I have never understood it, but 1/8 npt does look a lot like the 10mm thread shaft. Which goes along with:

Stefano, what do you think shows my picture?? The measured thread .
I should have said thread pitch. The diameter of the shaft is almost, or it seems exactly, the same.
 

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Ok, let´s state then : The thread size in the block (exhaust side / low pressure) and inlet side (measuring unit) BOTH share M10x1.

Low pressure sender has a tapered thread (1/8" NPT), while the measuring unit has a M10x1 thread and needs extra copper seal.
 

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1/8" NPT looks a lot like M10x1. D is 9.65 mm and pitch is .94 mm
1/8" refers to the tube size.
 

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I honestly cannot understand your first and second paragraph, hunt. They seem to be conflicting statements.
No, quite simple. BOTH threads in the block are origin M10x1. Both threads in the block are NOT tapered.

I know this because I'm always cleaning those threads with a rethreading tool. As well I've already used a new low pressure sender with M10x1 thread (from Volkswagen, different pressure warning figure) in combination with a copper washer seal to get it sealed.

An 1/8" NPT fits into the origin Alfa M10x1 thread, that's the conclusion.
 

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Are M10 and 1/8 close enough that they are interchangeable? All the mechanical gauges I find are 1/8 NPT But I assumed all the electrical sending units for gauges and waring lights are M10.
 

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I believe that you are ok threading 1/8" NPT into the pressure switch hole because someone before you has done it already and the threads are already distorted. It may not be such a good idea if you ever want to go back and use an M10x1.0 device
 
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