It belongs to a separate dimensional series with its own proportions, not simply a scaled-down standard nut.

At small thread sizes, standard proportions give a nut too small across the flats to grip and too thin-walled to handle.

The machine screw series is wider across the flats relative to the thread, and often lower in height.

That gives something a small spanner or nut driver can actually engage.

Because the series is defined separately, across-flats sizes do not follow the pattern of larger nuts.

It is a different standard rather than a different quality.

Small-nut across-flats sizes differ between standards more than larger sizes do.

A driver set built around one regional series will not cover another.

This is a familiar problem in instrument, electronics and appliance work where components come from several markets.

The thread may be identical while the hexagon is not, so a nut that fits the screw still needs a different tool.

Where a range of equipment is maintained, keeping both series of drivers is usually cheaper than the alternative.

Specifying the standard as well as the thread size prevents it in new work.

Light duty - reduced height means limited thread engagement, and the screws they pair with are light-duty too.

These are assembly nuts for panels, brackets, terminals and light components.

They should not be pressed into service as small structural nuts.

In their normal applications the load is well below capacity and this is not a constraint.

Where more capacity is wanted at a small size, a standard-series nut in the same thread gives more engagement.

Very small threads have limited capacity regardless of the nut, so the screw is often the governing part.

Steel, brass, stainless and nylon - and the choice is wider than at larger sizes.

Brass is common for machinability, corrosion resistance and non-magnetic properties.

Nylon nuts give electrical isolation and negligible weight, at much reduced strength.

Stainless resists corrosion but galls readily at small thread sizes, where there is very little material to lose.

Plated steel is the general default and the cheapest.

In electronics the isolation and magnetic properties often decide, rather than strength.

There is very little material in the thread, and stainless galls before it strips.

Galling cold-welds the thread surfaces under pressure, after which the nut seizes and neither part survives removal.

At small sizes the torque required to strip is low enough that a fingertip can reach it with a driver.

Power drivers make it almost certain unless the clutch is set very low.

An anti-seize compound helps, though at these sizes it can be more trouble than a different material.

Brass or plated steel is often the more practical choice where corrosion is not critical.

For volume work usually yes - loose nuts at this size are dropped and lost, which is a real cost.

Self-clinching nuts pressed into the panel remove the loose part entirely.

Cage and spring nuts clip onto a panel edge and stay put during assembly.

Threaded inserts and moulded-in inserts do the same job in plastics.

Loose machine screw nuts remain the right answer in repair, prototyping and low-volume work.

The decision is usually made on assembly time rather than on the fastener's cost.

On soft or thin material yes, and at this size the washer is often doing more than the nut.

Small nuts have very little bearing area, so they emboss thin sheet and plastics readily.

A washer spreads that load and prevents the nut pulling into the material.

On oversized or slotted holes a washer is essential, since the nut alone may not cover the opening.

Spring and tooth washers are common at this size for vibration resistance, since locking nuts are less available.

Adding a washer changes the grip length, so screw length should account for it.