Sterlingz
Sterlingz
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10 Aug 2018

Help with selection of fastener grade

Hi folks,

I'm at the last stage of engineering a sliding aluminum track which will be held down by bolts. I've selected a #10-24 x 2in size machine screw but am having a hard time selecting a bolt grade. I have some questions I'm hoping someone can answer;

1. Is #10-24 common enough that it can be found at hardware stores? Any reason to consider 10-32 (fine thread)?

2. Four grades available; 18-8, 316, zinc plated, black oxide plated. I read somewhere that stainless will corrode aluminum. Should I go with zinc plated then?

3. Is there a significant difference between 18-8 and 316 in terms of corrosion resistance? The final application will be marine environment, NO saltwater.

Thanks in advance!

10 Aug 2018

I have done some study on this issue. Please see below:

              1.   http://www.bssa.org.uk/topics.php?article=89

Excerpts from the above article:

Aluminium and stainless steel together also appears to be a bi-metallic corrosion risk, from the 'nobility' table.
With this combination the affect of relative surface area on corrosion is important.

A large area of 'cathode' relative to 'anode' will accelerate the anodic corrosion. Although aluminium is anodic to stainless steel, large relative surface areas of aluminium to stainless steel can be acceptable, dependant on local conditions.
Stainless steel fasteners in aluminium plates or sheets are normally considered safe, whereas aluminium rivets or bolts holding stainless steel parts together is an unwise combination, as there is a practical risk of corrosion.

2.      http://www.ajaxfast.com.au/downloads/AjaxRivetsHandbook.pdf

The table on page five of the above article shows Al rivets on SS are incompatible. SS on SS suitable.

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