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I checked my gauge with a variable resistance tester. Per that, Ed's numbers are spot on for my 78 Spider and 78 Sport Sedan.
 

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We’ll go figure, most of all my machining is for 2 German companies, all of there drawings with tapered threads required are NPT, the M10x1 are for there grease fitting nipples. On the Alfa blocks the tapered threads are NPT, if it has a machined flat surface they are 10x1 which require a copper sealing washer.
 

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1978 Spider
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Discussion Starter #83
, if it has a machined flat surface they are 10x1 which require a copper sealing washer.
excellent point....I have an after work project today...pulling the oil light sender back off and checking for a smooth machined sealing surface for the washer.

I was about to order a oil light new sender that appears to be M10...but it also shows thread sealant already applied (that dry red stuff)…

But just how is it that all the various sources of this oil light sender...some are M10 and some are 1/8NPT??? I see many with the sealing washer and apparently straight M10 threads...and many without but what appears to be a tapered thread. I'm pretty sure Alfa didn't switch back and forth all the time...Or are half the Alfa's out there running with the wrong sender installed?
 

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Put the threaded section into the jaws of a caliper and hold it up to the light. You will see a space between the jaws and the outer threads if it is tapered. I don't see how anyone can positively identify the thread by looking at a picture on the internet.
 

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Discussion Starter #85
No I cannot be positive from a picture. But some listings provide good clear, close up pictures of the threads. Some clearly show an included sealing washer. Some without the washer but still stating M10. Some do not provide clear pictures. Googleing certain brands & part numbers result in hits that mostly all specify M10x1.0....but a couple do state 1/8NPT, I think only on the Delphi brand sender...these companies have engineers figuring these things out and yet they still do not have 100% agreement...maybe 90% consensus?

 

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Push hard and live
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I’ve got a 78 2000 on an engine stand in the shop. I’ll check the low-pressure switch threads today or tomorrow.

If memory serves, the Spica fuel low-pressure light switch is a 10X1 straight thread. I wonder if the two switches are the same? I think the fuel trigger is 7 psi, which sounds about like the oil trigger as well.
 

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We’ll go figure, most of all my machining is for 2 German companies, all of there drawings with tapered threads required are NPT, the M10x1 are for there grease fitting nipples. On the Alfa blocks the tapered threads are NPT, if it has a machined flat surface they are 10x1 which require a copper sealing washer.
I mean, I guess it could be NPT? I'd just be surprised if they used any standard stuff in Europe. Usually when I talk to guys over there if I use any non-metric dimensions or standards they look at me like I have broccoli growing out of my ears (which is, in fact, the correct response.)
 

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I'm going from memory but I'm pretty sure at some point OP light switch was NPT, at least on the later cars, so there may be some grounds for confusion here.

On my '91 the light sender is attached to the block via an L-shaped brass adapter. The connection at the block is an M10x1 banjo bolt (with copper washer at the mounting surface) but the sender is clearly tapered thread. This is how the S4, at least, came from the factory. Found this photo that shows it, my car looks the same.

If the sender screws directly into the block it should be M10x1 straight thread, but not sure if that part is available. It looks like Classic Alfa EN057 is M10x1? Maybe ask them, they tend to be pretty responsive.
I am not totally convinced about that.
(Could be someone just screwed a NPT into that elbow)
this UK vendor has the original sender for the S4 spider (PN 60506902) and states the thread is M10x1
oil sender.jpg

and another seller
sender2.jpg

I'll have to check mine;)
 

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1978 Spider
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Discussion Starter #89
I'm gonna speculate that because of the NPT taper....that a 1/8NPT male can be "made-to-work" in a female M10x1.0 plug with the use of Teflon tape or other thread sealant...

But likely a 10Mx1.0 male likely cannot be fully threaded into a 1/8NPT female plug more than a couple threads before the taper narrows below 10M. Thus the sealing washer will never be compressed to seal...unless the M10 male is forced to turn tighter against the deeper and narrowing threads, effectively "re-tapping" the softer female metal from NPT taper to straight thread metric?

obviously neither is a good situation...but one is likely more damaging that the other?
 

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I was the instrumentation and controls engineer on a plant startup in France and all of the tapered thread fittings were NTP. Maybe they used tapered metric on the European space program.
 

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Discussion Starter #91 (Edited)
I think pretty much most all tapered pipe globally conforms to BSPT...which I think NPT is based upon but not exactly. I believe all Europe uses BSPT for tapered pipe. Maybe the Brits did tapered pipe first and exported to the world...a lot of things worldwide are based upon British standards...it was the empire whose sun never set...thus the standard was entrenched before metric could displace it. Sounds like a wiki search is needed...
I'd be willing to bet if there are tapered threads anywhere on the Alfa engine that they are BSPT...not NPT. but 1/8 in either is so close that no one ever noticed?
 

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Discussion Starter #93
On the Alfa blocks the tapered threads are NPT, if it has a machined flat surface they are 10x1 which require a copper sealing washer.
I removed my sensor and the surface appears flat. Not sure if 'machined flat"...after 40+ years the shiny smooth surface may have discolored and been marred by fitting previous sealing washers. here is a picture. And you can see the remaining gap when the NPT sensor was hand threaded into the hole. The threads are starting to bind at this point.
 

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e were having the same problem on our 74 GTV 2000, talk with Gordon Self, Just replace sender. Centerline, OP681 for Veglia Gauges $79.50 not for Jeager gauges)or OP685 for OP light (fine thread).
Good luck
 
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