Slots divide the crown into segments pressed inward, and they spring against the bolt as it enters.

The elastic reaction of the steel grips the thread, giving prevailing torque without any insert.

Because the deflection is elastic rather than permanent, the segments recover when the nut is removed.

That is why reusability is generally better than for a distorted thread nut.

The mechanism is entirely metal, so heat and chemistry do not affect it.

The grip exists whether or not the joint retains its clamping load.

The resistance only begins when the bolt reaches the crown, rather than applying along the whole engagement.

A distorted thread nut is loaded from the moment it starts, so every turn is hard.

A flexible top nut spins freely up the bolt and only the last part of the travel resists.

On long bolts that difference is substantial in assembly time and tool wear.

It also generates less heat in the threads, which reduces galling risk in stainless assemblies.

The locking performance is comparable, so the easier assembly is a genuine advantage.

Generally more than a distorted thread or nylon insert nut, within the manufacturer's stated limit.

The segments deflect elastically, so they recover their shape rather than being permanently deformed.

They do take a small permanent set over successive cycles, which is why a limit exists.

The criterion is the remaining prevailing torque: a nut that runs freely to the joint has stopped locking.

Bolt thread wear also accumulates, as with any all-metal locking nut.

Documented maintenance regimes may still specify single use.

Whatever the material and plating allow - there is no polymer element to soften.

That puts it alongside distorted thread nuts for engine, exhaust and process heat.

Solvents, fuels and cleaning chemistries do not affect the mechanism.

Ultraviolet exposure, which degrades polymer inserts over years, is irrelevant here.

Stainless and alloy versions extend both temperature and corrosion performance.

Very high temperature relaxes bolt preload over time, which no nut design solves.

Yes - a bolt that stops short of the locking segments engages nothing.

The locking section sits above the plain threaded portion of the nut.

A short bolt clamps the joint through the plain threads and never reaches the lock.

The nut feels tight, so the error is invisible once assembled.

The check is that thread is visible at or above the crown.

Bolt length is specified rather than taken from stock partly to prevent exactly this.

Better than a nylon insert, because the segments bear over a length of thread rather than relying on a clean path.

A nylon collar depends on the bolt cutting a clean channel through it.

Damaged or contaminated threads tear the collar and reduce the lock.

Metal segments bear on whatever profile is present and still develop grip.

Badly damaged threads should still be dressed or replaced rather than accommodated.

Grit in the thread invites galling in stainless assemblies whatever the nut type.

Where the very high prevailing torque along the full engagement is wanted, or where that type is what the specification names.

A distorted thread nut resists from first engagement, which some applications value.

Availability and cost also differ between the two by market and by size.

Where a specification names a class of prevailing-torque nut, that class is what should be fitted.

For severe transverse vibration, neither is as effective as a wedge washer pair or a positive lock.

For most all-metal locking requirements the two are practical alternatives, and assembly effort often decides.