The Good ol’ Standby Probably isn’t

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Adam Bahret

The good ol’ standby for locking nuts and bolts together has always been the split lock washer. Even if you are not an engineer, gearhead or craft hobbyist you have seen them a thousand times. Regardless of life style, apartment/condo dweller, you have restored three houses, or never moved out of your parent’s basement, you’ve seen one.  At some point in your life, you put together a piece of furniture, kids toy, new tool, or exercise equipment using split lock washers.

So, by the title of this article, you can foresee that I am not going to tell you that split lock washers are the #1 way to hold nuts and bolts together.  But, since we see them as the “go-to” they must be in the top five… right? Ok how about top ten? Really? Ok, so where do they rank?

I was recently revewing a guide NASA created back in 1990. It is based on a summary of internal studies on ways to use fasteners, and the key factor in fasteners is if they stay fastened. It was titled, “Fastener Design Manual,” NASA Reference Publication 1228, Richard T Barrett in case you want to look it up. (I ended going down a rabbit hole with this one and found a great video demonstrating and comparing one of the best locking methods, Nordlock, a great concept).  

So, where did our old friend the split lock washer come in among all the different options? Well, it didn’t. I don’t mean that they didn’t evaluate it, what I am saying is that they didn’t even bother giving it a score. In fact, it performed so poorly that their summary on it reads, “The washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a lockwasher of this type is useless for locking.”

That doesn’t even read like a technical analysis, it reads more like a burn coming from a teenager across a crowded cafeteria. I mean, “nonexistant ability” and “useless,” what worse thing could possibly be said to a piece of hardware? “Your Mom is so rusty that sandpaper uses her!”, “Your so screwed up that your Mom is metric and your Dad is standard!”, “Your weaker than a zip tie!” 

So if they are officially “useless,” and so many items we know are counting on them to stay together, why aren’t we seeing things falling out all over the place?  Wait, stuff is falling out all over the place.  Everyday furniture gets wiggly and needs to be tightened back up, they give you a wrench for this purpose, bicycles need to get a tuneup each spring, my lawnmower makes rattling noises until I can find out what needs a good torquing up. 

My best practice from years of turning wrenches on cars is that if I ever see a split lock washer, I apply Loctite (a chemical bonding agent for metal) to the threads before reassembling. 

Without this NASA study, we already knew it was a crummy fastener retention method.  So why is it still the largest quantity in the bin locking method next to the nuts and bolts found in all hardware stores?  All the other methods, that work to different degrees in the study, are considered “specialty” and are located in bags of small quantities high up on the wall. 

Simply put, I think it’s just a case of, “that’s what my Dad used, and his Dad before him, so that’s what I use.” Add in the factor of being inexpensive and you find your place right  in the big bin next to the nuts and bolts. 

That is by no means an uncommon phenomenon.

I see this all the time in product design, especially in determining factors in design for reliability. There are reliability goals, specific stress requirements, life cycle count limits, hours of use, and dimension tolerances all of which often have no known origin.

“It’s ok, it passed our specification.”  

“Where did that spec come from?”

The answer to these types of questions is usually along the same lines of “my Dad and his Dad but it’s, “my boss, who was told by his boss, who was told by his boss, who read it off a stone tablet that was handed to him by a guy wearing an animal skin breechcloth…”

Now, the consequence of doing it this way is not trivial. For example, there are product features out there that are 5X more reliable than they need to be, adding incredible cost.  We also have products out there that fail even though “they meet spec.” When the issued are root caused it is often miscategorised as being a quality issue or some other generic bucket. In that case, the issue is never solved and, eventually, the infrequent failure mode driven by so little margin is just considered the norm and accepted. The worst part is the outcome of it cutting into the business bottom line, brand credibility, and ultimately market share.

Here is what may be an interesting exercise for you to do: Buy a few members of your team lunch. Once they are settled in with full bellies, ask them to list five standard practices they use that they do not know the origin of. Is it unfair to say that you could easily have 20-50 best practices, standards, and guidelines on the board that have no known reason to be valid?  Would it be unfair to say that if even two of those are costing you money in “over-design” or a low-level constant field failure rate that you are hitting the companies bottom line with a $10 million annual loss?  

It’s an alarming thing to ponder.



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