NASA: Split Lock Washers Are "Useless"! - LinkedIn

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"I know we have a problem with loosening but I don't understand why...we use split lock washers everywhere".

This is not the first time I've had this conversation with an engineer, customer or even an experienced distributor. Engineers know a lot especially in their field but they don't always understand everything when it comes to fasteners - so when a bolted joint comes loose and they are using a DIN, ASTM or other standard "locking fastener" they scratch their heads.

I get it, its effectively a spring and pushes against both the nut and/or bolt and the work surface or flat washer placed on the work surface. The force it exerts on the work part(s), the axial load and the sharp edges of the cuts in the washer, that will surely prevent loosening - well, not really.

So often I talk to engineers and explain that there are many factors that contribute to loosening, and until that conversation the logic is - lets just throw on something that is called a lock washer and let it do exactly that, be a washer that provides locking. Well, there's your problem - they don't work! Don't take my word for it, here is NASA concluding they do not help prevent loosening and they have known about this for decades!

“The typical helical spring washer … serves as a spring while the bolt is being tightened. However, 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.”

- NASA Reference Publication 1228 (1990) “Fastener Design Manual”

NASA, these are the brilliant minds that send people into outer space. They put the lives of astronauts on the line and the futures of their families into darkness if things go wrong - because if something goes wrong, it really goes wrong BIG. It would make sense that they would invest time and money into making sure that every nut, bolt and washer is up to spec and does what it is supposed to do because they simply cannot afford an accident or a maybe.

Yes they are cheap but how does that help solve a problem if they don't work? There are a lot of locking fasteners out there; lock washers, lock nuts, thread lockers, pins, welds and others - how do you choose something that works for you and how do you know it will work in solving your problem?

First off, please do not use split lock washers to prevent loosening - don't.

The next step is to do your own research, understand the pros and cons of each option. There is no perfect solution, some locking fasteners work in some applications but not in others - for example you would want to avoid serrated washers in areas with extensive and repeated impact shock or substantial settling in the work part(s) or surface, but they might be fine for no or low vibration applications without impact shock or settling.

Talk to the company you are considering and of course they will tell you the benefits but, always try to understand the downsides or limits of each option - when is this option NOT suitable or when will it NOT work. This simple piece of advice most companies do not follow is a major reason split-lock washers are sold in in enormous quantities to end users that simply don't know any better.

Parameters to keep in mind when choosing a locking fastener are:

• Maintenance: Will this require a lot of regular replacement or repeated re-torquing. Is this a locking fastener that is known to come loose over time or has it been tested to stay secure even under vibration?
• Time: How long will this product last? How long does the installation/disassembly take?
• Effectiveness and Performance: Will it actually work in YOUR application? Will it work in the specific type of vibration you are dealing with and do you know what the different types of vibration are? Does the guy selling you fasteners know?
• Cause Of The Problem(s): Do you fully understand what is causing loosening in your joint and what result actually matters to you? Are you speaking with someone that can answer that?

Split lock washers are a discussion I've had many times, yet it never seems to go away. I have seen them used just about everywhere, I've found them coming loose in the gym, on bridges, tractors, mining equipment the list goes on. With time they will hopefully be used less and less, but in the meantime - be cautious.

If you found the above helpful, feel free to share it and leave a like or comment to let me know. To be notified of future articles, you are welcome to follow me and if you have questions or need input relating to this topic, feel free to contact me.

Written by Roger Bogrash, Director of Business Development @ CoiLok Locking Fasteners

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Split lock washers aren't just used due to historical inertia. A lot of times a split lock washer is enough to eliminate loosening in mild vibration. I can certainly point to several cases in personal experience where using split lock washers were helpful. Claiming split lock washers are completely useless is going to run counter to the experience of a lot of engineers you work with. There exist studies showing split lock washers do provide resistance to loosening under certain conditions. It is understood that vibration causes loosening of fasteners, but there is actually no consensus on the exact physical mechanism by which this happens and a half-dozen theories. So it shouldn't be surprising that what works in one situation doesn't work in another. If higher vibrational loads are experienced or it is an operational- or safety- critical component, I agree there are more effective solutions out there and split-lock washers offer pretty poor resistance to vibration compared to many other alternatives (especially if fatigue is of any concern here). But they've done a pretty good job of keeping those pesky bolts from loosening on my lawn tractor for 5 years now.

Like Reply 1 Reaction Zaid McAllister 2y

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Would have to disagree. The function of the split-lock washer is not only in its ability to dig into the metal surfaces. Some locking washers have no sharp edges at all. The function is to add tension to the bolt.

Like Reply 1 Reaction Nicholas Clesceri 3y

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Are wavy washers useful for locking fasteners?

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