Nut screws washer and bolts – you know the old joke

[Kiwi BlokeParticipant @kiwibloke62605]

It’s a bit late for me to be asking this question, having been manipulating nuts and bolts, in an amateur capacity, for well over half a century, but I still don’t really know when and why to use washers with threaded fixings. My library of engineering-related books doesn’t provide answers. I’ve seen plain washers used to protect surfaces, but have also seen bolt heads bearing directly on machined faces on castings. The application of spring washers makes some sense, but I’ve seen bolts with a plain washer under the head, with a spring washer and nut on t’other, and vice-versa, but rarely spring washers at each end. I understand that plain washers can be used to protect surfaces, and also to facilitate the turning of a bolt head or nut, and it makes sense to put a plain washer under the part that will receive the spanner – unless more resistance to accidental undoing is required. But practice seems variable.

On the face of it, the application of washers may be less complicated than I fear, as far as the resistance to turning of the nut or bolt with respect to the surface under it, but it then gets more complicated when applied to fixings that ‘lock’ the nut to the bolt, like Nylocs or other ‘stiff nuts’.

So, the questions remain: washer or not, which, where, and why? Is there an authoritative, accessible text, or is it more a matter of custom and practice (which may mislead, as in the lock nut position confusion – let’s not start that again!)?

[Andrew CrowParticipant @andrewcrow91475]

Let me first say I am no expert in this field, but I believe it is good practice to put a washer under the nut or bolt head that is going to tighten against the part being bolted to prevent damage.

When it comes to locking washers, many of these are designed to damage the surface to prevent loosening ie star and split spring washers, usually used to save cost.

If you need a locking method without damage then use a nyloc or locknut with a plain washer.

Andy

[Michael GilliganParticipant @michaelgilligan61133]

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 DonovanParticipant @alandonovan54394]

Hi.

I was taught that you should put the washer under the ‘moving element’ when tightening.  That could be under the nut or bolt head depending on the situation.

I did however often make judgements as whether a washer should be used at both ends – where either element could be the moving part.  Alternatively, thicker washers can have a ‘dual use’ as a load spreader over slotted holes or (slightly) oversize clearance holes for example.

Alan

[noel shelleyParticipant @noelshelley55608]

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.

[HollowpointParticipant @hollowpoint]

Not a technical answer by any means but here is where and when I use them.

A. To protect the surface underneath.

B. When the drilled hole is almost as big as the screw head

C. Load spreading. When the material doesn’t have enough strength. Thin box section or plastics for example.

D. Insulation. From electric, vibration etc.

E. Decorative. A countersunk screw cup type washer for example sometimes looks more professional than just a screw head.

[Nicholas FarrParticipant @nicholasfarr14254]

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.

[bernard towersParticipant @bernardtowers37738]

When at work (motor transport) it was flat washer ,spring washer, nut and god help you if you didn’t , I was under a lot of ex REME and Tank reg guys.

[Michael Gilligan]

On 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

[Robert Atkinson 2Participant @robertatkinson2]

I concur with hollowpoint and have following comments:

For normal use the washer goes under the part that is to be turned. So for nut and bolt under the nut.

Insulation can include galvanic corrosion e.g. using a plated steel washer between aluminium structure and a copper ground lug.

Robert.

[BazyleParticipant @bazyle]

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.

[bernard towersParticipant @bernardtowers37738]

wouldnt you have used wire locking for that?

[Nigel BennettParticipant @nigelbennett69913]

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.)

[Bill PhinnParticipant @billphinn90025]

When using Nordlocks with through-holes, the manufacturer’s advice is to use a pair under both the bolt head and the nut.

As for Nigel’s observation about colleagues not understanding their manner of use and using only half of a pair, I started a thread on here several years ago about my experience ordering Nordlocks from Zoro, where the warehouse team simply could not grasp that a quantity of one Nordlock washer consists of two halves. About four successive orders all contained half the number of washers they should have done. I got a refund, but had to give up in the end because it was clear their packers either would not or could not grasp the point.

Any coincidence Zoro UK are no more?

And, yes, Nordlocks are good, whilst spring washers aren’t very.

[Nicholas Farr]

On 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.

 

[duncan webster 1Participant @duncanwebster1]

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

[duncan webster 1]

On 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.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Bill, I’ve never seen or used Nordlocks, so can’t make any direct comment about them. Much of the plant I used to work on was made by Barber-Green, and neither did they or the company I worked for, seemed to have any need for them. The company had many vibrating sizing screens, one of which would screen about a Tonne of material, at about every 5 minutes, five days a week, with three shifts every day, and never really had any issues of things coming loose, one screen had two bearings of around 300mm outside diameter, in hubs of about 400mm overall diameter, without any locking arrangement on the the high tensile set screws that held them in place, and were torqued up, not once in the whole of my 36 years there, did they ever come loose, and I changed those bearings a few times, very often in the annual shutdown maintenance period. Don’t get me wrong, and I’m saying they are of no use, as I’ve seen many different ways of stopping nuts and bolt working loose. Very often, it’s the frequency of the vibrations that can make the difference, as I’ve seen lab equipment, where we’ve had to use a locking compound to stop things coming loose, most likely down to their design.

Regards Nick.

[duncan webster 1Participant @duncanwebster1]

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

[Bill DawesParticipant @billdawes]

I think the old joke originated around GKN, or as it was then, Guest, Keen and Nettlefold up in the Black country, a legend in the fastening industry.

Bill D.

[Howard LewisParticipant @howardlewis46836]

In my industry, we found that spring washers were not a reliable means of preventing fasteners  slackening.

Star washers were not popular, either, so never used.

Rolls Royce Oil Engine Division, did not go as far as the aviation side, in wire locking everything. But there were not many fasteners, on important areas, which were not locked with tab washers.

Leylands, particularly engines, could be locked in similar ways.

On ther chassis side, they tended to prefer a plain washer and split pin in a cross drilled hole.

With 1/2 UNF bolts, tightened into yield, there was no neeed for locking.  The thread fricion, fom the 9 ton load, would keep them tight for the life of the engine.

When I helped build a sports racing car, the engine components in vital areas, were wire locked.

Howard

[Gerard O’TooleParticipant @gerardotoole60348]

By coincidence, this double threaded bolt was featured on NHK news yesterday evening

ht, tps://www.nisseiweb.co.jp/pdf/FastenerTechnologyInternational202110.pdf

As I understand it, it uses two threads of different pitch to create the locking force. It is further refined in order to make assembly easier. The news item showed the making of the complex roller dies to roll the threaded bolts.

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