Well wire gauge is typically not how one would identify a bolt. Number wire gauge would typically be referred to by the units (either AWG or mm^2).
> If you are looking for fasteners for specific industrial use then I'd assume you would have the expertise to select the appropriate fastener or some internal engineering specification to follow.
Typically, yes although a friend was lamenting in the difficulty in finding a castle nut for an automotive application on the McMaster site.
> You don't just buy something from the scientific bolt category on Amazon. You may also require material certificates etc, which I don't believe is something these online options typically offer, though I may be wrong.
Well, McMaster offers will call (at one location) and offers phone support. The other folks Amazon is trying to compete with (Fastenal, Grainger, MSC) have a variety of B&M locations. I can't speak to material certification but I've purchased a certified caliper from Grainger no problem. Meanwhile Amazon still has the counterfeit issue to grapple with.
Castle nuts are a bit of an oddity too. Id assume your friend is possibly using them for trailer bearing retainers or possibly some really old suspension items. Not even sure there is really even a specification the ones available here seem to adhere to.
They are something I've generally gone out of my way to engineer out of a lot of applications as there is better options available.
Id imagine that the problem is that software engineers don't understand hardware engineering, and it's actually not a space where a lot of good resources exist. I.e. without a little bit of familiarity with material science and industry, it's not just something you can easily google. You need an engineer familiar with the fastener industry if you want a chance for getting a decent system of classifications.
Also from a metric country, things like number and wire gauges are odd to me as well as I only occasionally have to deal with them.
If you are looking for fasteners for specific industrial use then I'd assume you would have the expertise to select the appropriate fastener or some internal engineering specification to follow. You don't just buy something from the scientific bolt category on Amazon. You may also require material certificates etc, which I don't believe is something these online options typically offer, though I may be wrong.