Having worked in a vibration test lab, I will simply note that spring washers are generally less reliable than the myriad other locking arrangements.

MichaelG.

Alan has mentioned it – On some bolts or nuts where the tensile load is high the washer is use to spread the load and and may well be of a higher grade steel than a normal MS. This situation is common in the building of IC engines where the head and bearing cap bolts use a washers. May be Howard Lewis will join this one, he will know.  I’m not a fan of spring washers and they should never be used in electrical work, certainly if it is a high current !  Noel.

Hi, most washers are relatively soft, which allows them to deform to any unevenness between the bolthead or nut, or both, this is usually done where the surfaces around the holes have not been machined, which helps stop microscopic distortion of the bolt or a stud, and is often used where parts are dismantled and reassemble during maintenance periods, which also helps stopping distortion of the area around the holes. It is good practice in most cases, and will help to get the correct torque that is required. They are not absolutely necessary in all cases, but will help in tightening and undoing, and if you get a nut and bolt that refuses to undo, a washer will help stop damage to the bolted parts, if you have cut through the bolt with a grinding disc or a gas cutter. There are what are called hardened washers, which are normally used on vibrating machines with high tensile bolts, and where the parts have been machined flat, as ordinary washers will just creep under a nut and / or bolthead, and the assembly will become loose. Spring and star washer types are really only good where there is only a mild amount of vibration, and should only be used once, but self-locking nuts should also only be used once, but will stand up to much heaver and intense vibrations than spring or star washers will. It is of course, up to oneself to use washers or not on everything, and you my not need to use them under a bolthead, but I do in most cases.

Regards Nick.

On 18 July 2026 at 08:30 Michael Gilligan Said:

Having worked in a vibration test lab, I will simply note that spring washers are generally less reliable than the myriad other locking arrangements.

MichaelG.

Yep.

NASA guidance plain says simple spring washers don’t work for anti-vibration.
I also know of one case of an aircraft structural failure (wings came off a Tiger Moth) caused buy incorrect use of a spring washer (asymmetric load load on threaded connection) amongst other isssues (cut rather than rolled thread).

Robert

We used wavy washers for M3,4,5 nuts on MoD airborne equipment for ‘fast jets’. The testing was one hour on a sort of 3ft diameter loudspeaker coil driven from a 1 megaWatt generator. Of course anything that wouldn’t have to be taken apart for regular maintenance was threadlocked.

Years ago we had a chap visit us at work; he worked for Nord-Lock, who make anti-vibration washers. He gave a very impressive demo of the vibration resistance of plain nuts, lock nuts, Nylocs, nuts with spring washers, etc, etc, all torqued up to the correct figure. They all simply unscrewed under the applied vibration of a gizmo he’d brought. It was quite disturbing to watch them unscrewing within a few seconds! Then he fitted a nut with the Nord-Lock washers, which are fitted as a pair. They have fine serrations on one side and coarser, ramped serrations on the other. The fine serrations fit outside, against the job and the nut; the ramps engage with each other. Naturally, this nut just sat and laughed at the vibration. (I suppose the vibration frequency applied was carefully chosen, though, but still…)

As an advertising gimmick, the firm also sent out a piece of steel with a screw welded to it. It came supplied with a pair of Nord-Locks and a wing nut. It was very noticeable that it needed a lot more torque to unscrew the wing nut than to tighten it; in fact somebody broke the wing nut trying to undo it!

They use these things on pavement whackers and the like.

Anyway, we were sufficiently impressed with the things that we used them quite a bit in our firm’s products. We had to take care to spell out to our assembly shop and service documentation that they had to be assembled correctly and in pairs. We still found that some clown would chuck away one of the washers, thinking it was an unnecessary extra!

And no, I have no connection whatever with Nord-Lock! (Other manufacturers are available.)

On 18 July 2026 at 10:19 Nicholas Farr Said

most washers are relatively soft…It is good practice in most cases, and will help to get the correct torque that is required.

But not keep it, unfortunately, in the case of washers that are too soft, through embedment relaxation and loss of preload.

My apologies, Nick; I see you mention the place for hardened washers. However, contrary to what you also say, you can re-use Nordlocks.

On 18 July 2026 at 11:46 duncan webster 1 Said:

Out of interest I looked at the NordLock website, seems they supply the pair glued together now. Probably an attempt to overcome Nigel and Bill’s problem

Not really, Duncan. The glue isn’t at all tenacious; it can’t be otherwise the washers wouldn’t work as intended. As a consequence, pairs subject to any amount of movement in storage are susceptible to separation.

This is a good explanation of why bolts vibrate loose, and some don’t