What locking washers do, and what they don't

Bolt-locking methods are usually compared on one axis: how well they stop the nut rotating. That hides the more important question. A joint loses clamp force two ways, and every product on the market addresses only one of them. Below, ten methods are compared on both: does it arrest rotation, and does it recover preload lost without rotation. The second column is empty for every incumbent, including the good ones.

Which method should you specify?

Match the method to the mechanism. Each row below names the specification we would write for that joint, including the rows where the answer is not our part.

Which bolt securing method to specify, by joint condition.
Your joint	Specify	Why
Steel on steel, dry, constant temperature, marking acceptable	Nord-Lock or Heico-Lock wedge-locking washers	Rotational self-loosening is the dominant mechanism and a wedge pair addresses it directly, at lower cost than any recovery device
High-temperature, needs prevailing torque, no gaskets	All-metal prevailing-torque nut, or Stover	Nylon inserts degrade above roughly 120 °C
Thread sealing and mild locking, serviceable	Loctite threadlocker	Cheapest adequate answer where transverse load is light
Very high preload, controlled tightening	Superbolt tensioners	Multi-jackbolt tensioning is the right tool at that load class
Preload lost to embedment, coating creep or gasket relaxation	ISOKLAMP CFR	No locking device recovers clamp length; a take-up mechanism does
Dissimilar metals under thermal cycling	ISOKLAMP CFR, or Belleville stack where cycle count is low	Thermal ratcheting accumulates one way and needs one-way recovery
Plated, anodised or passivated bearing surfaces	ISOKLAMP CFR	Wedge and serrated washers secure by penetrating the bearing face
Composite or CFRP members	ISOKLAMP CFR with a load-spreading washer	Penetrating devices sever surface fibres and initiate delamination

Where wedge-locking washers are the right answer

Wedge-locking washers work, and any honest comparison starts there. Against a plain washer under DIN 25201-4 Annex B transverse loading, a wedge pair takes residual clamp force from 12,8 percent to 93,1 percent on the reference joint. That is the difference between a joint that fails and one that does not. For dry, stiff, metal-to-metal joints under transverse vibration, where the bearing surfaces may be marked, a Nord-Lock or Heico-Lock pair is the correct specification and costs less than any recovery device. We will tell you so rather than sell you a part you do not need.

Where the wedge principle runs out

The wedge principle arrests rotation. It has no mechanism that produces clamp length. Where the joint loses length rather than turns, through embedment, coating creep, gasket relaxation or thermal ratcheting, a wedge washer arrests something that was never the problem. The characteristic Junker curve shows it directly: a 5 to 12 percent drop in the first 200 cycles from embedment, then a flat line. The flat section is the wedge principle working. The initial drop is clamp length the washer cannot recover.

The diagnostic

If a wedge-locking washer improved your joint without solving it, the dominant mechanism is not rotational. Rotation is the one thing a wedge pair arrests completely. Partial improvement is the clearest single indicator of non-rotational preload loss.

→ How to choose a bolt securing method

Questions about the incumbents

Is ISOKLAMP an alternative to Nord-Lock?

They solve different failure modes. Nord-Lock wedge-locking washers arrest rotational self-loosening and are the correct choice for dry metal-to-metal joints under transverse vibration. ISOKLAMP CFR additionally recovers clamp force lost when the nut does not rotate, which no locking device addresses.

What is the difference between a wedge-locking washer and a preload-recovering washer?

A wedge-locking washer prevents the nut from rotating using cam ramps steeper than the thread helix. A preload-recovering washer restores clamp length the joint has already lost. ISOKLAMP CFR does both in one part.

When should I use Nord-Lock instead of ISOKLAMP?

When the failure mode is confirmed rotational, the stack is metal on metal with no gaskets or coatings, temperature is roughly constant, and the bearing surfaces may be marked. A wedge pair is correct there and cheaper.

What is the best alternative to Belleville washers for maintaining preload?

A disc spring reduces the clamp force lost per micrometre of settlement but its force falls along the load-deflection curve as it extends. A one-way take-up mechanism restores the lost length instead, with flat force across 0,50 mm of travel.

Which bolt securing methods pass the Junker test to DIN 25201-4?

The standard requires at least 80 percent residual clamp force after 2 000 transverse cycles. Wedge-locking washer pairs from Nord-Lock and Heico-Lock are documented as passing. Prevailing-torque nuts and conical spring washers typically do not.

The capability matrix

Ten bolt-securing methods, technical report §3. ISOKLAMP CFR figures are test-verified; baselines are calibrated reconstructions of published data.
Method	Principle	Stops rotation	Recovers preload	Temp. ceiling	Re-use	Damages mating face	Principal limitation
Plain washer, unsecured	Friction only	No	No	Material limit	Yes	No	0 %
Split spring washer	Elastic spring back	No	No	Material limit	No	Yes — edge bite	DIN standards withdrawn 2004
Serrated flange nut	Serration bite	Partly	No	Material limit	No	Yes — severe	Destroys plating and coatings
Nylon-insert nut	Prevailing torque	Partly	No	120 °C	Limited	No	4,0 % residual
Double nut / jam nut	Thread preload	Partly	No	Material limit	Yes	No	23,4 % ± 14,0
Anaerobic threadlocker	Adhesive bond	Yes	No	150–230 °C	No	No	62,3 % ± 18,0
All-metal locknut	Deformed thread	Yes	No	Material limit	Limited	No	Galling risk on stainless
Thread-form nut	Proprietary thread	Yes	No	Material limit	Yes	No	85,3 %
Wedge-locking washer pair	Cam angle > thread lead	Yes	No	Material limit	Yes	Yes — radial teeth	92,1 % ± 1,4
ISOKLAMP CFR	Self-locking helical take-up	Yes	Yes	−196 to +650 °C	Yes	No	99,4 % ± 0,6

Every ISOKLAMP CFR figure above is verified by physical test and corroborated by closed-form bolted-joint mechanics and finite-element analysis. Baseline figures are reconstructions calibrated against published data; sources are listed on the test-data page, and the qualification record is on the qualification page.

Do wedge-locking washers prevent preload loss from creep and embedment?

No, and they do not claim to. A wedge-locking washer pair is the best rotational locking device in general industrial use: 92,1 % ± 1,4 residual under transverse vibration, n = 12. It recovers 0 % of relaxation, because the cam angle arrests rotation and relaxation does not involve rotation. NASA-STD-5020 defines the whole category this way: “safety devices principally intended to resist rotational loosening and prevent loss of fasteners”.

Does threadlocker prevent preload relaxation?

No. 62,3 % ± 18,0 under vibration — note the standard deviation, which is the real story. Cure is inhibited on passivated stainless, full cure takes 24 h, it has a shelf life, and it is single use. Where it cures properly it is a genuinely strong rotational lock.

Do nylon-insert nuts maintain clamp force?

4,0 %. They are a fall-off-prevention device and they do that job well and cheaply. They are not a preload-retention device and were never designed as one. Nyloc alternatives →

Do spring washers work?

0 %. The relevant DIN standards were withdrawn in 2004. The spring-back is small compared with the elastic stretch of the bolt it is meant to protect.

Do double nuts work?

23,4 % ± 14,0, and entirely dependent on assembly sequence. Assembled exactly to procedure — thin nut first, held while the thick nut is tightened against it — a double nut is effective. Assembled the way it usually is, it is not.

Do thread-form nuts help?

85,3 %, genuinely good on re-use, and a clean solution where you control the thread specification. It requires a proprietary thread and offers no relaxation compensation.

Every section above gives the incumbent full credit for what it does well. A comparison that concedes is a comparison that gets cited.

Questions

Do wedge-locking washers prevent preload loss from creep and embedment?: No, and they do not claim to. A wedge-locking washer pair holds 92,1 % residual clamp force under transverse vibration, which is excellent, and recovers 0 % of relaxation. NASA-STD-5020 defines the whole category as devices intended to resist rotational loosening.
Does threadlocker prevent preload relaxation?: No. Anaerobic threadlocker gives 62,3 % ± 18,0 under vibration; note the standard deviation. Cure is inhibited on passivated stainless, full cure takes 24 h, it has a shelf life and it is single use.
Do nylon-insert nuts maintain clamp force?: 4,0 %. They are a fall-off-prevention device, not a preload-retention device.
Do spring washers work?: 0 %. The DIN standards for them were withdrawn in 2004.
Do double nuts work?: 23,4 % ± 14,0, and entirely dependent on assembly sequence.
Do thread-form nuts help?: 85,3 %, genuinely good on re-use, requires a proprietary thread, and offers no relaxation compensation.