A wedge or collar is drawn against a tapered seat as the joint is tightened, deflecting inward onto the thread.

The locking force is therefore generated by tightening rather than fixed at manufacture.

It increases with preload, so a properly tightened joint locks harder than a loose one.

The clamping acts over an extended thread engagement rather than at a single deformed section.

That distributes the locking load and is why they perform well under high-amplitude vibration.

Different manufacturers implement the principle differently while the mechanism is the same.

Continuous high-amplitude vibration, and joints that cannot be inspected often - heavy plant, rail, mining, crushing and marine.

In those conditions single-point prevailing-torque nuts can lose grip as the joint works.

Nylon inserts are often ruled out by temperature before vibration is even considered.

Inaccessible joints justify a more capable fastener because the maintenance cost of reaching them is high.

For ordinary machinery within reach, a distorted thread nut or a wedge washer pair is usually sufficient.

The decision is normally made on consequence of failure rather than on vibration alone.

Generally yes, within a stated number of cycles - the components deflect elastically rather than deforming permanently.

That is a real advantage over distorted thread nuts, which take a permanent set.

Manufacturers publish both a cycle limit and a minimum prevailing torque.

As always, a nut that runs freely to the joint has stopped locking.

Components must stay together as a set; mixing parts between nuts is not acceptable.

Given the cost per piece, reusability is a meaningful part of the economics.

Incorrect orientation or seating of the components, which produces a nut that locks nothing while looking normal.

The parts have a designed relationship, and assembling them the wrong way round defeats the mechanism.

Many are supplied pre-assembled for exactly this reason and should not be taken apart.

Seating the collar against its taper requires the joint to be tightened properly; an under-tightened joint under-locks.

Manufacturers publish installation instructions that are specific to their design rather than generic.

Because the failure is invisible, following those instructions matters more than with a single-piece nut.

Both work by geometry rather than by fixed friction; wedge washers are cheaper and work with standard nuts.

A wedge washer pair uses cam faces steeper than the thread pitch, so backing off tightens the bolt.

A multi-piece nut clamps the thread itself over an extended engagement.

Wedge washers mark the joint faces with serrations; multi-piece nuts generally do not.

Wedge washers are far more widely available and much less expensive.

Where a serration-marked joint face is unacceptable, the multi-piece nut has a clear advantage.

Yes - prevailing torque must be added, and it may vary with the design more than for simpler nuts.

Some of the effort goes into forming the locking action instead of into clamping the joint.

Manufacturers publish prevailing torque values specific to their product.

Because the locking force increases with preload, under-tightening reduces both the clamp and the lock.

That makes correct torque more important here than with a fixed-friction nut.

For critical joints, angle-controlled or tension-indicating tightening is preferable.

They are specialist products - availability, lead time and size range are all narrower than for standard nuts.

Most are proprietary designs sold by their manufacturer rather than as a commodity.

That means the installation data and the replacement parts come from one source.

Lead times matter where a maintenance stock has to be held for inaccessible joints.

Sizes outside the common industrial range may not exist at all.

Establishing availability before specifying avoids designing around a nut that cannot be obtained.