Only as part of a temporary works design that specifies them - improvised prop strutting is a well-known and dangerous practice.

A prop is a single compression member, not a support system.

Trench support requires spacing, bearing area and load paths that a design establishes.

Props bearing directly on a soil face concentrate load and punch in.

Where props do appear in trench support, it is between walings or panels that spread the load.

Purpose-made hydraulic shores exist precisely because they are engineered for the job.

A longer prop buckles at a lower load - capacity can fall several times over the extension range.

Buckling capacity of a slender member drops rapidly as its length increases.

That is why rating tables are printed on the prop rather than being a single figure.

Using a long prop at short extension is safe; using it near maximum extension is a different product entirely in capacity terms.

Choosing the shortest prop that reaches is the practical rule.

Reading the table on the prop takes seconds and is skipped constantly.

Loading a prop off its axis - it carries far less and can fail suddenly rather than progressively.

Props are designed for axial compression through the centre of the head and base.

An off-centre load introduces bending, which a slender tube resists very poorly.

Props set at an angle need proper head and base fixings designed for that arrangement.

Uneven bearing surfaces produce eccentricity without anyone intending it.

Failure under eccentric load tends to be sudden buckling rather than gradual settlement.

The pin carries the entire load between the inner and outer tubes, and substitutes bend.

Reinforcing bar, bolts and improvised pins are all commonly seen and all wrong.

The correct pin is a rated component supplied with the prop.

A bent or missing pin means the prop cannot carry its rated load and may collapse under it.

Pins are lost constantly on site, which is why they are worth stocking as spares.

Checking the pin is present and correct is one of the fastest checks available.

Bent tubes, damaged threads, corroded collars and missing base plates - all visible and all reduce capacity.

A bent tube has already buckled once and will do so again at lower load.

Damaged or clogged threads prevent the collar developing full engagement.

Corrosion at the collar is common because props are stored outdoors.

Missing or bent base plates concentrate load and introduce eccentricity.

Props live hard lives and are frequently the least-inspected item on a site.

Bracing formwork, supporting temporary works, and strutting between walings within a design.

Formwork for walls, columns and slabs is the largest single use.

Temporary support during structural alterations is another common application.

In excavation work they appear as struts between designed waling arrangements.

Push-pull props with fixings at both ends are used for plumbing and holding formwork.

In every case the load path is designed rather than assumed.

Heavy-duty props, shoring towers and proprietary propping systems, all with published capacities.

Standard adjustable props have modest capacities, especially extended.

Heavy-duty props and proprietary systems carry substantially more and come with design support.

Shoring towers and frames spread load and suit greater heights.

For structural propping, the temporary works designer specifies the system rather than the site choosing it.

Mixing systems or substituting components between manufacturers invalidates the published capacities.