Water Temp Sending Unit Question(s)

[VFilms]

I replaced my 2brl intake with a '56 Poly 4brl intake.
The threads on the water temp sending unit that came out of the 2brl intake measure 3/8". The thread size on the 4brl intake measures 1/2".
I'd like to replace the sending unit without having to use a reducer (1/2" to 3/8"). Anyone know if they're are available.
Also, all listings I find for these sending units list 1/8 NPT thread. So I did a little reading up on NPT threads and now I'm really confused.

 

[69Bee]

National Pipe Taper (NPT) means that the plug forms a threaded taper with the largest diameter at the top of the hole. NPT sizes (Bottom, Middle, Top) are as follows:
1) 1/8"NPT is 0.365"/0.375"/0.405"
2) 1/4" NPT is 0.478"/0.490"/0.540"
3) 3/8" NPT is 0.612"/0.627"0.675"
4) 1/2" NPT is 0.758"/0.778"/0.840"

The numerical size does not represent the actual size of the hole you see. You likely have 1/8"NPT on the 2BBL manifold and either a 1/4"NPT or 3/8"NPT hole on the 4BBL manifold. Hope this helps...

 

[VFilms]

National Pipe Taper (NPT) means that the plug forms a threaded taper with the largest diameter at the top of the hole. NPT sizes (Bottom, Middle, Top) are as follows:
1) 1/8"NPT is 0.365"/0.375"/0.405"
2) 1/4" NPT is 0.478"/0.490"/0.540"
3) 3/8" NPT is 0.612"/0.627"0.675"
4) 1/2" NPT is 0.758"/0.778"/0.840"

The numerical size does not represent the actual size of the hole you see. You likely have 1/8"NPT on the 2BBL manifold and either a 1/4"NPT or 3/8"NPT hole on the 4BBL manifold. Hope this helps...

Helps a great deal! Thanks for the information.
EDIT: So, in reading your chart, the 1/4" NPT is 0.478"/0.490"/0.540" which shows a 0.540" top measurement, will equate to roughly a 1/2" (0.500') threaded hole in the manifold, which is the size I have. Makes sense.

 

[1967coronet]

Helps a great deal! Thanks for the information.
EDIT: So, in reading your chart, the 1/4" NPT is 0.478"/0.490"/0.540" which shows a 0.540" top measurement, will equate to roughly a 1/2" (0.500') threaded hole in the manifold, which is the size I have. Makes sense.

Just remember you are installing a wedge with a NPT fitting / pipe.
Easy to crack a side if over tightend.