What exactly do them numbers mean, I know what the quarter inch means but whats the -20. Btw this is for a pyrometer probe. Do i just need a 1/4inch NPT tap?

 

I'm not sure but I believe that the 20 is how many threads per inch there are?
you will want an NPT tap for the pyro. Just don't take it too deep or your fitting will never get tight. I'm not sure if 1/4 inch is your size. I don't remember what size I used on mine.

 

1/4-20 is a screw that is 1/4" in diameter, and the 20 is threads per inch. m6x1.25 is 6 millimeters in diameter, and the 1.25 means the thread pitch is 1.25 millimeters (thread peaks are 1.25 millimeter apart). You don't want to use either of these for your pyro. It will be 1/4-18 npt. Which is 1/4" tapered pipe thread with 18 threads per inch.

 

Ptm hit the nail on the head. Pipe threads are tapered unlike screw or bolt threads. The pyro is usually 1/4 or 1/8 inch pipe threads.

 

"This includes a basic K type thermocouple probe that can be used on small vehicles. The probe has M6x1.25 thread that also fit with ¼-20 English thread. Cable length, 78” (2 meters). Maximum working temperature: 1000C (1800F)"

I already bought it. What exactly is going to happen? So I don't drill it out to a NPT like usual for a pyrometer? I just drill it out like a regular bolt hole now or what?

I know your explaining it correctly I just don't understand.

 

Does it use some sort of jam nut? That's about the only way I think a straight thread could be used in this application. Do you know what brand it is?

 

Spot on post, use a 1/4-18 npt tap, it will look awfully big as compared to what you think, however it is the correct size.


Tim

 

If you are going to tap for either a 1/4-20 or a m6 x1.25, the tap drill is #5 (.205). Hope this answers your question.

 

So can i use a 1/4-18npt for this? Or am i reading that wrong?

If i use a 1/4-20....what will be the negative effects?

 

I believe most type K probes are 1/4-18 npt. The only other size that it might be is 1/8-27 npt. If it is, the threads on the thermocouple will look alot smaller in diameter than the tap. 1/4-20 is alot smaller than either 1/4 npt or 1/8 npt. You should be able to tell the difference by comparing the threads on the thermocouple to a tap.

 

DO NOT use a 1/4 20 tap, you are suiciding yourself from the get go, as previously stated it is 1/4-18 npt. Hold one against the other and you will see for yourself.


Tim

 

You guys saved me from going out and drilling a new hole that wouldn't work! Then I would of had 3 holes as I'm keeping my old 1/8in pyrometer hole just plugging it off! I understand now, I was just confused as there were a few different answers being given.

Thanks

 

I would be willing to bet it is a Npt threads on that thermocouple unless it is something special. My autometer was 1/8-27 npt just went and looked on the tap i used. But remember you could order a 1/4-18 if you prefered. It was adjustable though so that it used a second compression nut to thread on top and wedge the the therocouple since it was adjustable up or down in the bushing depending on your mounting depth you wanted it but both were pipe threads.

 

Why not drill though the 1/8" hole?
Then you'll only have one hole.