Supra Forums banner

drill and tap size for "1/8 NPT"

12783 Views 4 Replies 3 Participants Last post by  mysupratt
No it's not 1/8 :D

I'll be installing my Greddy EGT probe. What is the drill size I need and the tap size for 1/8 NPT?

1 - 5 of 5 Posts
The tap drill size for 1/8 npt is a "Q". You would then tap it with a 1/8npt tap. "Q" tap size in decimals is .3320 inches. The npt taps are different from standard taps in that npt taps are tapered. Hope this helps.

John B.
Thanks guys. Just came back from Orchard Supply, the packaging on the 1/8 NPT tap actually tells you which drill size to use...11/32. :) Now, I'll just have to find a shop that can do TIG welding.
Ummm.... isn't 11/32 too big for a 1/8npt tap??

5/16 has worked perfectly for me. The tap I use recommends a 21/64 bit but I'd rather go a bit smaller and give the tap more metal to dig into.
1 - 5 of 5 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.