Help identifying thread

[Rex Walters]

Sure looks like a pipe thread to me.

BSPT 3/8 is 19 TPI.
NPT 3/8 is 18 TPI.

Seven threads are visible. What’s the distance between the crests of the first and the last?

 

[AllenV]

good use for a thread guage

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[Rex Walters]

good use for a thread guage

Except none of us are quite sure what "20G" really means on his gauge...

That's why I suggested simply measuring with calipers to see if it's really 20 TPI.

 

[Jake M]

Sure looks like a pipe thread to me.

BSPT 3/8 is 19 TPI.
NPT 3/8 is 18 TPI.

Seven threads are visible. What’s the distance between the crests of the first and the last?

That is indeed the pitches for 3/8 pipe under both standards. That thread though is 5/8 of an inch in diameter. The thread in question is 3/8 of an inch in diameter. 27 or 28 threads per inch. Or 20 threads per inch if it's a British standard fine thread. Here's a size reference. Sorry, I don't have any British pitches at my disposal, but the diameters are consistent either way.

 

[Rex Walters]

19 and 18 tpi would be 3/8 pipe sizes. All NPT variants an both BSP variants use those threads. That's in the neighborhood of 16mm outside diameter. The OP has measured 9.45mm outside diameter on the mystery threads. His measurement is within a fractional millimeter of 1/8 pipe thread in either system, That's where the 27 and 28 tpi comes from. Or a 3/8 BSF bolt thread, which would be 20 tpi.

I’m confused (1/8, 3/8, 5/8? 18, 19, 20, 27, or 28 TPI?) and should bow out, but here’s what I’m taking as givens:

- the photo appears to show a taper which indicates a pipe thread.

- it measures 20G on his gauge. I don’t know if that means 20 TPI, but the pitch at least is easy enough to measure.

- OP measured 9.45mm dia which is near as nuts 0.375” or 3/8”. Unsure which end of the taper this was taken on.

- the drill size for 1/8” NPT or BSPT is 21/64”, so it makes sense to me for a male plug to measure about 3/8” somewhere along its length (the drill diameter is slightly smaller than the threads on the male part.

- but 1/8 BSPT is 28 TPI and 1/8 NPT is 27 TPI. Those threads in the photo don’t look that fine to me (could be wrong), and it seems odd a gauge marked 20 G would (nearly?) match 27 or 28 TPI.

So confused.

But I still think simply measuring the distance between 7 threads is the easiest way to determine the actual TPI for certain (hopefully 27 or 28TPI).

 

[RJSakowski]

Except none of us are quite sure what "20G" really means on his gauge...

That's why I suggested simply measuring with calipers to see if it's really 20 TPI.

I am not sure what the G stands for but I have a similar thread gage and the 20 is 20 tpi.

 

[RJSakowski]

Fitting a new sender to the oil filter housing won't be that difficult. I would most likely go the route of making an adapter to accept an 1/8 -27 MPT. The should be hundreds, if not thousands, of oil pressure senders with 1/8-27 threads.

The difficult thing will be matching a new sender to the dash gauge. All the senders that I have run across reference to make and model of vehicle. none of them give any information as to the internal workings of the sender. The best bet would be to get involved with one of the Land Rover forums. Someone there will have blazed the trail for you.

 

[francist]

Looks like the “G” may be the designation for a Whitworth thread. See chart below…

 

[Rex Walters]

See chart below

Wait. There are “Whitworth” and “British Whitworth” designations on that chart.

Does that mean there is a non-British Whitworth thread form?!!

Aaaaaaaaaaah!

As they say, the great thing about standards …

 

[francist]

Good question, and I’m beginning to think I should never have opened my mouth!

I don’t know that there would be British and non-British Whitworth but rather that the Whitworth pattern was adopted into formalized thread forms such as the BSW and BSF.

There is also the British Standard Pipe (BSP) which also uses the Whitworth thread form. Interestingly enough, when I looked it up (Wikipedia) there was a small footnote explaining the origins of the “G” and “R” abbreviations for this system: they originally stem from the German for “gas” and “pipe” which, given that the verso side of the original gauge in question had “Metrisch” (German for “metric”) may at least explain that part.