Westach Gauge Installation

[EBolgiano]

Hopefully someone who has installed the Westach EGT gauge will be able to answer a question. The instructions for the 1/8" probe say to drill a 5/16" hole and then to tap it with a 1/8" NPT pipe tap. Is this correct? I have not looked at the 1/8" NPT tap but, 5/16 is 2 1/2 times as large as 1/8. I would like to get the gauge installed today but I can wait until Monday and call Geno's. Thanks in advance for the help.

 

[Thomas]

The tap drill for a 1/8-27 NPT is letter drill R (. 339" diameter). The 5/16 Westach is suggesting is . 3125" diameter.

Here's what is available from 5/16 to letter drill R:

5/16 = . 3125
"O" = . 3160
"P" = . 323
21/64 . 328125
"Q" = . 3320
"R" = . 3390

The 5/16 will work.

Your bigger concerns will be hole location & how far you run the tap in. The threads are tapered and running the tap in more turns will increase the diameter of the threads.

 

[Joe G.]

5/16 is 2 1/2 times as large as 1/8.

The confusion might be because pipe is measured by the size of the ID.

 

[EBolgiano]

Thanks for the info Thomas. Sounds like you are either a machinist or some type of engineer. And Joe G you are absolutely right about the ID. I studied Mechanical Engineering at LSU and have a machinists handbook stored somewhere. I'm sure the wife knows exactly where it is located. Hopefully I'll get the gauge installed today. Thanks again.