Using Stainless Steel Fasteners
For vintage and classic restorers and owners the stainless steel nut, bolt and washer has become fashionable for their low maintenance shining silver colour and not just because they have a superb resistance to corrosion and load bearing capabilities in all weathers.
Be careful though as there are problems and mistakes made when using them that could cause lasting damage.
Choosing the wrong grade
Simply put 316 grade stainless steel has the same corrosion resistance as yellow chromate on zinc plate. It is the reason it is more expensive than 306 grade stainless steel which shows corrosion twice as quickly, about the same as blue chromate on zinc plate.
​
Keep clear of 400 and 200 series stainless steel fasteners, especially studs. There are a lot of unreliable sellers out there that sell cheap stainless steel fasteners that corrode quickly. The problem is you cannot see any difference between the various grades of stainless steel making it advisable to buy from a reputable dealer.
​
Putting stainless steel next to aluminium or zinc helps corrosion
In damp or wet conditions, stainless steel next to aluminium or zinc corrode faster. It is not the stainless steel that corrodes first, it is the zinc and then the aluminium. It’s not just on the surface either, a threaded hole in an aluminium case with a stainless steel stud will corrode as far down as the moisture goes, weakening the thread.
​
The corrosion does take years and it does need to get at least damp every so often. As soon as it is dry the corrosion slows down but when a vehicle is put away for years people forget. The shed leaks, the tin roof sweats and drips, it was stored straight after washing without drying. Winter road salt, sea air, spray or in sea itself are the worst conditions.
​
Treating the nut, bolt, or the washer with one of the modern, thin film, ceramic type of protection coatings will help stop corrosion. Rubber or plastic washers or seals can also help but only when moisture is completely stopped from getting through. A nut and bolt with rubber or plastic washers do not stop moisture from travelling along a thread.
​
Another alternative is to use a zinc plated washer or a zinc plated stud and when it starts to rust, strip clean, replace for new and protect with oil, wax or one of the newer corrosion protection coatings. The zinc washer is sacrificed and tells you that corrosion is occurring.
​
Metal particles or dust helps corrosion
The outside of a fastener can become contaminated with metal particles and dust from grinding, polishing or the action of a brake pad wearing a brake disc down. These fine particles and dust can contaminate the outside of a stainless steel fastener and when damp cause corrosion to occur more quickly.
​
Long periods between cleaning helps corrosion
Stainless steel needs to be cleaned frequently to keep contaminants such as metal particles, metal dust and chemicals from settling on the surface. The vapour or gas from battery acid is another common contaminant as it turns to moisture on the surface of a fastener. These contaminants slowly change the appearances of the surface, and it becomes more difficult to retain the original finish as the corrosion sets in.
Regular cleaning will help protect stainless steel fasteners but then make sure that they or the vehicle they are attached to is dry before it is stored away.