Moving the trailer at all - it cannot be towed, rolled or manoeuvred by hand, whatever is done to the coupling.

A coupler lock stops the trailer being hitched, but the coupling can be attacked, cut off or replaced given time.

A clamped wheel cannot rotate, so even a defeated coupling leaves the trailer where it is.

It also stops the trailer being manhandled onto a low trailer or pushed away, which a coupler lock does not.

The two are complementary rather than alternatives, which is why valuable trailers carry both.

Neither defeats a crane or a flatbed with a winch, which is what ground anchors and secure parking address.

For a trailer left unattended, yes - otherwise the wheel can be removed and the clamp goes with it.

A clamp that only bars the wheel against rotation is still attached to a wheel that is held on by nuts.

Removing those nuts takes a socket and a couple of minutes, and the clamp leaves with the wheel.

A covering design encloses the nuts so they cannot be reached, which removes that route.

Full-face and shrouded clamps go further and cover the whole wheel, leaving nothing to grip or lever.

For a trailer clamped briefly in a supervised yard the distinction matters less; for one left overnight in the open it is the whole question.

By tyre size and wheel width, and it is a real constraint - trailer wheels span a very wide range.

Manufacturers specify a range of tyre sizes each clamp fits, and it is narrower than people expect.

A clamp too large for the wheel can be rocked and worked off; one too small will not close.

Wheel width matters as much as diameter, particularly for covering designs that have to sit over the face.

Protruding hub caps, bearing caps and deeply offset wheels can all prevent a covering clamp seating properly.

Check against the actual wheel rather than the trailer model, since wheels are frequently changed over a trailer's life.

Frequently - several markets have independent rating schemes, and policies may specify a level as a condition of cover.

Rating schemes test resistance to attack with defined tools over a defined period.

A rated clamp differs from an unrated one in materials, lock mechanism and the absence of easy purchase points.

Policies for trailers, caravans and plant frequently name a scheme and a level, and cover can be affected if the device does not meet it.

Some policies also require the device to be fitted whenever the trailer is unattended, not merely owned.

Requirements vary by jurisdiction and insurer, so check the wording rather than relying on a general standard.

Weight and stowage - a strong clamp is heavy and awkward, and if there is nowhere to carry it, it stays in the store.

Security comes largely from mass and hardened material, so an effective clamp is genuinely heavy.

It has to travel in the towing vehicle, and if there is no proper stowage it ends up loose in a load area or left behind.

Fitting one in the wet at the end of a shift is a real disincentive, and compliance falls quickly.

Fleets that mandate clamps without providing stowage and a simple procedure end up with unused clamps and unprotected trailers.

Choosing a clamp that is quick to fit, and giving it a dedicated place in the vehicle, does more for actual security than choosing a heavier one.

Barrel lubrication, checking the mechanism operates, and keeping the contact surfaces clean - plus protecting the wheel from the clamp.

Clamps live outdoors and in vehicle load areas, so their barrels seize like any other outdoor lock.

Use a lock-specific lubricant on the barrel and keep any weather cap in place.

Check the adjustment mechanism still moves freely; threaded adjusters in particular corrode and jam.

Grit trapped between the clamp and an alloy wheel scratches it, so wiping both before fitting is worth doing on anything with a finish.

Inspect for damage after any attempted attack, and replace rather than repair a clamp that has been cut or deformed.

Yes - they are also used to prevent unauthorised movement of trailers and plant on site, which is a safety measure rather than a security one.

An unattended trailer that can roll or be moved is a hazard on a sloping or busy site.

Clamping a trailer taken out of service prevents it being coupled up and used by mistake, which is a genuine risk in a fleet with shared equipment.

The same applies to a trailer awaiting repair, where a clamp plus a tag is a clear physical indication that it must not be used.

Clamps do not replace chocks and a properly applied parking brake, which are the correct devices for preventing roll.

Where a clamp is used to take equipment out of service, record it, or it becomes a trailer nobody can find the key for.