Thread identification please

[RonA]

Can anybody identify a thread for me.
The thread is in a pocket to allow fitment of a temperature measuring bulb.
As near as I can measure the thread is 0.654” across the peaks & 18 TPI.
Checked my Zeus book but nothing close.
Thanks in anticipation
RonA

 

[Rannsachair]

Could it be a tapered thread? 3/8 NPTF is 18 tpi and a female thread id of .63.

 

[RonA]

Could it be a tapered thread? 3/8 NPTF is 18 tpi and a female thread id of .63.

No its definitely parallel but could it be as you 3/8 But parallel?
RonA

 

[Rannsachair]

No its definitely parallel but could it be as you 3/8 But parallel?
RonA

Looks like 11/16 SAE, handy reference: https://www.hydraulicsdirect.com/Fitting-Thread-Chart-s/1934.htm#NSPM

 

[bricol]

Look up the spec of the temp sensing bulb and see what thread that is as a starting point?

 

[RonA]

The threads on your link seem to tally with my measured thread Thanks
RonA

Look up the spec of the temp sensing bulb and see what thread that is as a starting point?

Slightly tricky, its on car that dates from 1934
RonA

 

[bricol]

The threads on your link seem to tally with my measured thread Thanks
RonA

Slightly tricky, its on car that dates from 1934
RonA

That would have been useful info at the beginning

 

[clift_d]

Slightly tricky, its on car that dates from 1934

I'm afraid you can't drop a statement like that without pictures to back it up.

 

[RonA]

I'm afraid you can't drop a statement like that without pictures to back it up.

Posted this several times b4 as its progressed, but this is how it stands at the moment RonA