Its forming teeth or sprung arms either cut a thread into the shank or bite into it and hold.

Thread-forming types roll or cut a mating thread as they are turned on.

Push-on speed nuts have sprung arms angled so they slide on in one direction and dig in against withdrawal.

Neither needs any preparation of the stud beyond a correct diameter.

The saving is the whole thread-cutting operation on the mating part.

In volume assembly that is a substantial cost and time reduction.

Modest retention loads - they hold a part in place rather than clamping a joint to preload.

The load path runs through relatively thin sprung or formed material.

There is no meaningful preload, so the joint is not clamped in the way a conventional assembly is.

Manufacturers publish push-off and torque values, and they are much lower than an equivalent threaded assembly.

Anything structural, calculated or safety-related needs a conventional nut on a proper thread.

Within their intended duty they are entirely reliable and enormously cheaper.

In practice no - many are designed to be destroyed on removal, deliberately.

Removing a push-on nut bends the sprung arms permanently, so they no longer grip.

A thread-forming nut that has cut its thread will not recut it consistently in the same place.

For assemblies never meant to be opened, that permanence is a feature rather than a limitation.

Where a joint must be serviceable, a conventional threaded fastener is the right choice from the start.

Replacement nuts are cheap, so destroying one during a repair is rarely a problem.

Push-on speed nuts, thread-forming nuts and sheet-metal spring nuts - one idea, three quite different products.

Push-on nuts snap over a plain stud and are held by sprung arms.

Thread-forming nuts roll or cut a mating thread as they turn onto a plain shank.

Spring nuts clip over a panel edge or into a hole and receive a screw that forms its own thread in the pressed opening.

The last of these is really a captive nut rather than a locking nut, though it is sold in the same family.

Which is appropriate depends on whether the mating part is a stud, a shank or a panel.

Very - too small and the nut spins, too large and it cannot be driven.

The nut is designed around a specific shank diameter and a tight tolerance on it.

A plain rod cut to length is easy to get wrong, particularly if it is drawn or extruded stock with a loose tolerance.

Surface finish matters too, since a very smooth shank offers less for sprung arms to bite.

Manufacturers state the acceptable shank diameter range explicitly.

Checking a sample before committing to a production run avoids an expensive discovery.

They resist withdrawal well and rotation less so - the mechanism is aimed at retention rather than at preload.

Sprung arms angled against withdrawal make pulling the nut off difficult.

There is little clamping load, so the usual vibration-loosening mechanism does not apply in the same way.

Continuous vibration can work sprung arms loose over time, particularly on a smooth shank.

For a joint that genuinely vibrates and carries load, a conventional locking nut is the correct answer.

For trim, covers and light retention they perform well in service.

Appliance, automotive trim, furniture, electronics and packaging assembly - anywhere volume and speed dominate.

Trim panels, badges, clips and covers are held this way in enormous numbers.

Furniture assembly uses them where a fixing must be quick and is never disturbed.

Electronics enclosures use spring nuts to give a thread on thin sheet without a press operation.

Packaging and display fixtures use push-on nuts for the same speed reasons.

They are rare in maintenance work precisely because they are not designed to come apart.