i need to buy a nut to weld on to my turbo straight pipe for the o2 sensor/ does anyone know what size hole is has to be to screw the 02 in to it?

91 civic hatch, homemade turbo+ LS motor = 12 sec street car.

18 mm, say size as a standard spak plug, lol.

I think it is 19mm.I bought O2 bung at a muffler shop for $2.00. You may want to try that if you can't find a nut to fit.

I'm pretty sure it's an 18mm x 1.5 thread

13.5 @108 MPH-2.2 60ft(stupid FWD!)
S16G @ 18 PSI/FMIC/Running on MegaSquirt II (Now with sequential
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-1998 Mitsubishi Eclipse RS-T- "Toy"
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-2000 Honda CR-V(daily)

ok and what size socket is best for removing the o2 on our cars? i know honda takes like a 22mm or so.

91 civic hatch, homemade turbo+ LS motor = 12 sec street car.

If i remember right it is a 23mm. You will probably need to use a boxed end wrench or an O2 sensor socket.

Im positive it is this. It is an 18mm.