Stainless Steel Hardware, Galling, Anti Seize and Nylock Nuts

Actually my fingers are a little bit on the weak side. I assume that not only was the tread cut with a worn out tap but the captive nut was probably also filled with kind of a "fish scale" of micro galling flakes. I probably got a mechanical lock when I turned the screw in by hand and then complicated it with some fresh galling when I tried to back it out.

I have not had a lot of luck with recommendations. Galling seems to be very dependent upon the grade of the stainless, the match/difference of stainless grades, the quality of the thread and possibly the alignment of the stars, is Elvis in the house, etc.

You forgot Mercury in Retrograde.

My oversight. Thank you for the correction.

Thanks for the reply. I suspected that the nylon should wipe the threads pretty clean but I still worry about it.

We have often used the same stainless for both the bolt and the nut. A few days ago I read on http://www.estainlesssteel.com/gallingofstainless.html that the grades of stainless should be different. I'll add that to my bag of tricks in the future.

Beware of the cheaper stainless fittings - many seem to be produced at too fast a speed and as a result the threads are not smooth. I had issues where assembly of a machine frame went easily, but the bolts needed cut off due to the severity of the galling. To eliminate this, further bolts from the same batch (we only used around 10 per 3-6months from a bag of 50) were cleaned up with a die before use. Next batch were bought elsewhere at double the price, but with no issues.

The worst of my problems were with "cheaper than cheap" hardware installed by a sheet metal shop that I will resist the urge to name. It appeared that the nuts were made with either a worn out tap or a tap with a broken tooth. In addition, they were trying to install cheap Chinese captive nuts in a stainless steel enclosure. In an attempt to keep them from spinning it appeared that they may have been pressing them in with too much force. Thus, I suspect that I may have had a fractured and flaking galled surface inside the nut before I installed the screws.

The 1/2"-13 hardware on tower mounted equipment would have been reasonable quality hardware (McMaster Carr, MSI, Bolt Depot, etc.) but would have been matching grades of stainless installed dry. It seems that having the bolt and nylock of different grades of stainless installed with anti-seize should work. I still worry a little about the nylock and anti-seize but everyone seems to agree that the nylock will hold.

Galling with stainless is always an issue or seems to be. I have solved some issues in insisting on a ( Mechanical Certificate ) be issued with regards to the product I am purchasing. Get this on both the bolts and the nuts as they may come from different sources and be different grades. Nylocks work well even with the anti seize compound if properly manufactured. In hardware there is a lot of sub standard product on the market and only a proper testing procedure or a mechanical certificate will give a heads up to a potential problem.

Good suggestion but for a lot of people it would be hard to enforce a policy where mechanical certs are needed.

One can experience galling/siezure of SST fasteners regardless of whether the bolt and nut are the same or different grades.

The best solution I have found over the years is to mechanical zinc plate (mechanically galvanize) the SST nuts. This provides a lubricant without reducing the thread clearance and eliminates any possibility of galling/siezure regardless of the tightening method. It also eliminates the need for any additional anti-sieze compounds.

I guess that explains why I have seen tin plated stainless steel rivet nuts.

Thank you for the comment. I know it is serious and valuable. But somehow I can't resist a small laugh at the idea of galvanizing stainless steel. I understand the value of doing it but it reminds me of the ____ (fill in your preference)____ that was so proud of the gold medal that he/she won at the Olympics that he/she had it bronze plated and placed on the wall next to the bronze plated baby shoes.

I worked in the bio-med field and had a major problem with stainless steel hardware. I got the best answer from Ohio Bolt who stated that hardware that had non-corrosive qualities also had a natural protective finish that caused the locking effect when the nut was tightened on the bolt. One company used a silver plating finish on their insert anti-vibration nuts stainless steel nuts. They produced stainless steel band clamps for exhaust plumbing. I did not find an anti-seize compound that was effective. I started using plated steel nuts on stainless steel bolts.

I like getting a paycheck so I won't ask them to buy me silver plated stainless steel hardware.

Exhaust plumbing in the bio-med field could mean a lot of different things. Did you have hardware problems when using anti-seize recommended for stainless steel hardware? I was surprised that getting a well known manufacturer to state "recommended for stainless steel hardware" was more difficult than I expected. Did you switch to plated nuts after one or two tries of whatever anti-seize was handy or did you have a good quality anti-seize that was recommended for stainless but failed?

Was there anything unusual about your application? Was it room temperature, outdoors, salt water exposed or exposed to incinerator temperatures?

This may be elementary, but remember to reduce your torque when using anti-seize so as not to over stretch your bolts (or damage the threads that you took pains to protect!)

Good suggestion, thank you. Sometimes I excel at focusing on the tough stuff and forgetting the simple stuff.

look for a different suppler. i buff the thread if i encounter a single thread problem, but i think your assumption with die problems is correct.