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Rave About Your Rack Please do not post retail SPAM.

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Kong vs Black Diamond 6-Dec-2006 At 5:53:39 PM tmarsh

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I don't think what you're saying is correct, Sceptic.

The bottom line with 3-sigma rating is that it means that 99.87% of the articles produced will not fail at a load under the rated load. Or to put it another way, 99.87% of the items are stronger than the rated load would imply.

The other testing method is simply the mean failure strength of the batch. What this means for the consumer is that 50% of the items will fail below the rated strength, and 50% will fail at loads above the rated strength.

As far as I know, all manufacturers who pursue a 3-sigma rating system advertise as such. The reason is that it is very expensive to test and certify to this extent. I've spoken to a guy from DMM who talked in terms of hundreds of thousands of dollars in implementing 3-sigma testing and a fairly major ongoing commitment to random batch testing. No-one's going to put in that sort of investment and not try and get some mileage out of it.

Having said that, I don't disagree that for practical purposes it's not going to make a whole lot of difference to most people in most circumstances. Arguing about 3-sigma ratings on biners for example is a little artificial, given the breaking strength is already way above what a human could survive if they were the thing causing the impact. Nuts and cams? It's not so out of expectation that someone could put a small nut close to its rated strength in a fall. Would you rather the 99.87% or 50% rating then?

But as you point out, Sceptic, this debate kinda assumes that the nut is placed perfectly. Maybe you'd be better off buying the cheaper nuts and put the spare change into learning how to place really good gear!