Water neck thread size?

Location
NE Ohio
I am trying to replace the coolant temperature gauge. I cannot figure out the thread size of the port.
Thanks in advance!

Seems too tight for a 3/8”
And way too loose for a sparex gauge I bought from NAPA.
 

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Pretty sure it is 3/8 inch NPT. What the pitch is I would have to get my gauge which is in the shop. The only trouble I have seen is the capillary tube is a little too long on some gauges.
 
That is not pipe thread, look at the differences in thread count in those pictures.
And look (zoom in) at the senser bulb, It has a male tapered flange that the threaded hex head part pushes against to seal against a female tapered seat in the cast iron.
The threads are not doing any sealing like NPT does.

I think.
 
I am trying to replace the coolant temperature gauge. I cannot figure out the thread size of the port.
Thanks in advance!

Seems too tight for a 3/8”
And way too loose for a sparex gauge I bought from NAPA.
Let's back up a bit, tell us what you are working on.

What tractor is this engine in?

What is the engine make and model?

If the sensor bulb in your picture is the one you took out, that may need a special/ specific gauge as it appears the seat for the bulb made in the hose neck.
 
Thanks for all the input and advice!
It is a 5/8-18 UNF thread!
I searched all over and ended up at Auto Zone.
I found a kit that has multiple bushing adaptors.
Let's back up a bit, tell us what you are working on.

What tractor is this engine in?

What is the engine make and model?

If the sensor bulb in your picture is the one you took out, that may need a special/ specific gauge as it appears the seat for the bulb made in the hose neck.
1953 TO30 Z129 The one in the pic is one I'd like to install. There is a seat in the bore, but also a seat in the bore of the adaptor.
 

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He has asked questions about 1953 TO30 in the past.
TO30 should have Z129 Continental gas. Pictures above seem to bear this out.
Yes you are correct! This is my very first tractor that had to sit when it went down a few years back and now I'm working to get it back into working condition. Hopefully going to brush hog and disc and move round bales (in a pinch). A friend replaced the clutch and the old temp gauge could not be removed resulting in cutting the tube.
 
Thanks for all the input and advice!
It is a 5/8-18 UNF thread!
I searched all over and ended up at Auto Zone.
I found a kit that has multiple bushing adaptors.

1953 TO30 Z129 The one in the pic is one I'd like to install. There is a seat in the bore, but also a seat in the bore of the adaptor.
The bulb is supposed to go in and seat without an adapter. The threads on the nut that holds the bulb in are supposed to fit the neck threads. The Equus gauges I have purchased have NPT bushings and one M16 x 1.5 bushing with a sealing ring to go under the hex of that bushing. I doubt there is a 5/8-11 adapter there.
 
That is not pipe thread, look at the differences in thread count in those pictures.
And look (zoom in) at the senser bulb, It has a male tapered flange that the threaded hex head part pushes against to seal against a female tapered seat in the cast iron.
The threads are not doing any sealing like NPT does.

I think.
Do you normally use tape or other sealant on these?
 
If I got screen shot to attach properly you will see 3/8 npt is .050 larger than 5/8 unf. You say Ferrel on capillary tube is too loose a fit into housing. I wonder if someone ran a 3/8 pipe tap in to install tank heater. Tell us if your adapters help.
 

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If I got screen shot to attach properly you will see 3/8 npt is .050 larger than 5/8 unf. You say Ferrel on capillary tube is too loose a fit into housing. I wonder if someone ran a 3/8 pipe tap in to install tank heater. Tell us if your adapters help.
I tried a 5/8 SAE bolt to verify the size and it was a great fit. I went to Auto Zone and picked up an adaptor kit with a 5/8 male end. The adaptor that actually fit best was the M16x1.5 that Jim.ME suggested. Not sure why its such a weird thread size on an otherwise very standard tractor. But, this thing will definitely be worth all the effort!
 
The bulb is supposed to go in and seat without an adapter. The threads on the nut that holds the bulb in are supposed to fit the neck threads. The Equus gauges I have purchased have NPT bushings and one M16 x 1.5 bushing with a sealing ring to go under the hex of that bushing. I doubt there is a 5/8-11 adapter there.
What Jim said. An adapter shouldn't be needed. At least for Stewart Warner and Autometer.
 
It is a Sparex from NAPA. Supposed to be compatible with a 35.
Most if not all guages don't use the adapter. I can't speak for junk guages. I'm not saying what you bought is junk. Do you have a picture of the bulb?

The bulb in the picture should screw right into the neck. No adapter needed.

Picture added
 

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16mm is .004 thousands larger than 5/8 inch
1.5 is16.9 TPI versus 18TPI ,with a little forcing it should go together.
Some capillary tubes are too long and need to be spaced back a we bit
when used in Ferguson.
 

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