I hear everyone saying the isspros have 1/8th inch pyro and boost taps, and my invoice syas I got an 1/8inch thermocouple and boost, but they look bigger than 1/8" where do they get the 1/8" from inside diameter, my supposedly 1/8" thermocouple is more like 1/4" outside diameter? EXPLAIN!

 

Probably 1/8 NPT thread

 

Shovel is right, all pipe thread is measure by the inside diameter of the pipe.

 

Untill you reach 14"...then it is the outside diameter

 

i've never really worked on anything that is bigger than 4"npt so i didn't know that...

 

1/8'' Pipe tap drill size is a letter "R" drill or .339 dia.
You probably don't have a "R" drill but a .344 11/32 is close enough

 

Hmmmm 14" are you thinking of upgrading that 5" dual exhaust........

 

So the 11/32 bit will work then?

 

for the 1/8" npt tap, it will work just fine... that is what i used... i have used 5/16" before too with suscess

 

side by side, 1/4 NPT and 1/8 NPT look close, but there is a difference. If in doubt, buy an 1/8 X 1/4 Reducer bushing and tap it 1/4".