Nut size for the O2 sensors please! (3 Viewers)

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May 30, 2008
After being a Northerner for decades, I is now a T
Regarding the O2 sensors that sit in the exhaust pipes just before the converters (I presume I have an FZJ80 series as it was manufactured in 1994, VIN begins with JT3DJ81W2R) - heard a lot of exhaust sounds, checked and found one O2 sensor dangling - the nuts that secure the thing had become undone! Post threads off the pipe feel clean. I think this O2 sensor was replaced about a half year ago, but the person who did the work is far enough away not to pester, and further complication is that we took the vehicle in for an inspection which it failed, so the problem could have been originated there also. In any case, I just want to fix it.

I tried to get an array of metric nuts from Home Depot, and it seems that the 8mm are the right size, but neither the 8mm-1 00 nor the 8mm - 1 25 fit the threads (the latter comes the closest. Can anyone tell me just what size I need to get for it?
Are you telling me that the 8mm 1 25 should fit? The threads inside them are brand new, and those on the post feel very clean, but certainly could be dirty enough to create a problem; however, first I kind of want to know, dirty or not, if I have the correct pitch/thread count or not (and size for that matter...)!
Clean the threads with a thread chaser. Mike


The stock Toyota studs are M8 1.25 pitch. The nuts from Cruiserdan are a copper material if I remember correctly. It takes a 12mm spanner or socket to remove; preferably 6-pt.


8x1.25mm, washer-base.
Not sure what kind of nuts these are, but I have replaced the O2 sensors before, and if you reuse the nuts (as the PO probably did), you may end up loosing the O2 sensor as you did some time later.

After loosing one sensor, I found that the nuts had simply backed off and the sensor just popped off after the nuts came out. There are quite a number of similar posts here on the same situation. These are not just Home Depot metric nuts that you can buy...the Toyota O2 sensor nuts are a variety that are somehow manufactured to be resistant to remove. There are cuts in the top of the nuts, almost like what you'd find in a castle nut, though much finer, and the effort to put them on is noticeably greater. If you're going to replace or reattach your sensor, I'd suggest replacing with the correct nuts so you don't end up blowing one off down the road again.

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