drill and tap size for "1/8 NPT"

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.

11/32 drill bit.

-TY

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.