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Dissimilar metals (threaded inserts/ bolts)

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  • Dissimilar metals (threaded inserts/ bolts)

    I searched this forum but found question relating to stainless steel and aluminum.....however my question is; Will I have a problem using brass threaded inserts with stainless steel bolts? I am building a patio table that will be exposed to the elements. Thank you! Marty

  • #2
    Re: Dissimilar metals (threaded inserts/ bolts)

    possibly, but should not be near as bad a with aluminum, on this page it show the potential of corrosion the further apart on the charts the more likely they will not play well together, I would suggest some anti seize compound, one designed for stainless steel,
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    • #3
      Re: Dissimilar metals (threaded inserts/ bolts)

      You may have a problem, but it should be minor.

      "Stainless" steel is so-called because in reality, the surface corrodes very quickly into a film that is pretty much moisture proof, and as such acts like a very fine paint coating. This is called "self-passivation" in which the metal protects it self. This same film will also insulate the brass from the stainless alloy, so it will inhibit most dissimilar metal corrosion (that is also why stainless fasteners work better in aluminum than regular steel ones).

      For most dissimilar metal applications, stainless is considered to be an inert metal. I say most because in the presence of salt laden moisture, or chlorine environments (i.e. swimming pools), the salts or chemicals destroy the passivating film as well as provide a very conductive electrolyte, so active corrosion can then take place.

      First, don't try to "clean up" any dull film on the stainless. That is the self-passivating coating.

      Second, Installing wet with a light coat of varnish, boiled linseed oil, etc (relatively soft coating), will further seal the threads from any moisture, and will still allow you to remove the fastener. The anti-seize compound will also work well for this, and is probably the best thing to use if you plan on semi-frequent disassembly. Vaseline will work in a pinch, but may leak out in the heat of the summer sun.

      If it is a permanent installation and you want to be sure it is sealed, coat the threads with epoxy, but don't plan on getting them back apart.

      You will probably have less problem using the stainless fasteners, than if you used brass ones, because the moisture in the threads will eventually allow the brass to corrode to itself, and the difference in oxygen concentration between the part in the insert and the part in the wood will also corrode the fastener. Being in Wisconsin, the stainless fastener/brass insert is probably the best combination to use.

      Hope this helps

      Last edited by Gofor; 09-13-2008, 07:41 PM.
      Practicing at practical wood working


      • #4
        Re: Dissimilar metals (threaded inserts/ bolts)

        Thank you so much for the help and explanation! It is of great help. Marty