Technical Brass nuts

I head that you should use brass nuts on exhaust bolts but my bolts are stainless. Guy at the hardware store said never mix stainless and brass. Is that bs?

 

Shouldn't be an issue. What you don't mix is a stainless with stainless- it can gall and basically lock up the threads. But with stainless studs, you can use steel nuts.

 

Generally, stainless and brass when in direct contact can result in corrosion.

In actuality, it depends on the grade of stainless as they can have significantly varied electrical potential.

If your bolts are a 300 stainless (like 304), you'll be much less likely to see significant corrosion than if they are a 400 stainless (like 410).

 

Galling is combated with anti-seize, also using steel with stainless as you mentioned can help.

 

Brass doesn't rust and is softer than steel, both good reasons to use on exhaust.
The nut being sacrificial if something happens is good practice.
Doing a search for "never mix stainless and brass" came up with this. They discuss fittings, not fasteners and how to mitigate the issues.
https://idealbelltechnology.com/can-you-mix-brass-and-stainless-steel-fittings/

 

I use a lot of stainless hardware (exhaust system included), most of it polished and expensive. I have had to cut a lot of bolts off that I installed just for mock up during construction! Anti Seize is your friend, use it liberally any time you grab stainless hardware. Never used brass nuts other than on a coil.

 

There’s a ton of mopars that had brass exhaust nuts from the factory.

 

I only use stainless on non structural items such as trim or cosmetic items

 

Brass is more anodic than stainless..

When you put brass on stainless, it can cause galvanic corrosion, and corrode the brass.

 

Yep, people are always amazed how fast stainless can gall. It happens very quickly.

 

Three conditions are needed for galvanic corrosion: dissimilar metals, electrical contact (meaning direct or close contact so electrons can flow), and an electrolyte (salt water or moist air, usually).

Today, I finally fixed the massive exhaust leaks on my classic foreign daily driver and used brass nuts (on steel studs).

 

The brass nuts you need are "brass manifold nuts", they are longer than the usual nut.

 

The OP is just outside of LAKEland.

 

I used to buy regular steel exhaust studs that came with brass nuts. They always came off.

Now I use all stainless with never seize.

 

Most of the galling that takes place with stainless fasteners is because the wrong grade of stainless was used....

 

The thing is, the grade of the stainless fasteners you find at the local hardware store is usually a mystery.

 

Agreed. I get mine from Allen's Fasteners where I know what I'm ordering and receiving.
https://www.allensfasteners.com

 

I know that Ford in the late '40's used brass nots on exhaust manifolds

 

I always use the long brass nuts on exhaust manifolds, with steel studs.
Is anti-seize even able to withstand the high temps of an exhaust manifold in the long term?

 

Regular old Permatex antisieze is rated for use up to 1600 degrees F, you can also get high temp antisieze that's good to 2500 degrees or more.

 

The OP is in the Florida panhandle. I don't know if the high humidity alone would be a catalyst for galvanic corrosion, but I'm fairly certain that the salt-air environment is. It seems that using brass nuts in those conditions would go against the purpose- preventing them from seizing on the studs. Maybe he can run an experiment.

 

Model A Fords came from the factory with brass nut's on the manifold to muffler clamp.

 

And as you know SS is not impervious to rusting, some are much better at resisting rust than others, I can't remember the grade numbers, many are in Chinese now!

 

It is well established that people who drive MOPARS need brass nuts.

 

I remember I once used some bronze nuts on my flatty exhaust. No problems. Use anti-seize.

 

304
18-8 is regular hardware grade
316 is marine grade

Most are from all over. China, Taiwan, some USA. I get them from Mcmaster Carr or Bolt Depot.

 

I don't think galvanized corrosion is an issue. As stated by sgtlethargic, there really is not any electrolyte available. As example do any of the zinc plated bolts on your engine have galvanic problems? No they don't, even though zinc is anodic to the iron (steel). Same basic situation with brass nuts, being anodic to the stainless steel. Unless your engine lives in water environment there just isn't an electrolyte. BTW, steel nuts are anodic to stainless as well; just not as much potential between them as compared to brass.

 

Chemistry is governed by the Laws of Physics, and wastes no time considering the opinions of mankind.

 

Atmospheric moisture, and precipitation are electrolytes.

You, and your vehicle are never not exposed to electrolytes.

http://pubs.usgs.gov/wsp/1535g/report.pdf

 

Yep. the ferritic grades have more iron and less nickel and chromium and do rust as well as the martensitic grades in the 400 series that have more carbon and are heat treatable.