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Oxygen sensor FAQ's :
Q: Are all oxgen sensor thread sizes the same?
A: There is only one exception that we are aware of it is an older Japanese sensor that used two bolts to hold a flanged sensors into an exhaust pipe.
These 2 bolt sensors are quite rare and never used for wideband sensors, they are quite unusual and obvious.
All other sensors, including stock narrowband and wideband sensors use the same industry standard 18mm x 1.5 mm thread.
18 mm is the O>D of the thread and 1.5mm is the thread pitch distance.
Q: Do I need a stainless steel or mild steel oxygen sensor bung?
A: It is possible to weld either mild steel bungs to stainless or visa versa, however if you have stainless steel exhaust you would not be keeping the original corrosion resistance that the
stainless exhaust sytem is capable of. In the case of welding a stainless bung to a non stainless exhaust that is perfectly fine, but of no extra benefit.
Welding stainless to mild steel can be done with stainless rod/filler metal or regular steel filler metal, of course you will have best corrosion resistance with stainless rods.
Q: How do I know if my exhaust is stainless?
A: There are many different types of stainless, however there are mainly only 3 types used in the Automotive industry.
NON Magnetic Stainless: 304 stainless,polishes well and is good for all normally aspirated engines up to a certain temperature, Most aftermarket stainless exhaust are
made from 304.
321 stainless,more expensive than 304 has titanium as a stabilizing agent allowing higher temps without cracking. Use this for pre turbo and rotary engines
exhaust (near the ports) because of high temps. Normally 304 series bungs are welded to 321 stainless even in high turbo heat areas. This is allowable
because the bung is so much thicker than the header tubing. Heck even a mild steel bung will survive longer than a header tube normally.
To summarize the main purpose of 321 is enhanced cracking reistance in high heat situations . Cracks are onky common in stressed areas not a bung to tubing weld for example.
Magnetic stainless 409 this is magnetic and has a slight brownish tinge as soon as it weathers at all, on older vehicles it will be a more rusty brown. It actually IS a very light rust
(oxide ) coating that prevents further rust. 409 is found on many vehicles from the factory. 304 bungs work well with 409 also.
First check if your exhaust is magnetic, if not it is defintley stainless. If it is magnetic it is either plain (mild)steel or 409 stainless. Keep in mind some fabricators use mild steel flanges and
stainless tubing. If it is non magnetic and has a silver "aluminum like" coating and some rust spots it is probably aluminum coated mild steel. If it is lightly brown everywhere with no real
rust it is probably 409 stainless.
CAUTION !!! some motorcyles have Titanium exhausts, these are not magnetic either. The way to tell (other than the price ;-) )is to use a grinder on an inconspicuous spot, the sparks will
be very white if it is Titanium, also it will be incredibly light weight. Titanium is not weldeable by most people and you will need a Titanium bung not stainless ot mild steel.
If you make a mistake in material identification it's not the end of the world as a bung usually lasts as long as your car !
When in doubt choose the stainless bung. Most shops/tuners who stock a bunch of bungs just stock stainless since it covers all applications.