In a single operation that slits and stretches simultaneously. The sheet feeds into a press with an upper die carrying a row of angled knives. On each stroke the die cuts a row of staggered slits and, in the same movement, pulls the material down and forward so those slits open into diamonds. The sheet advances and the next stroke cuts an offset row.

Because the cutting and the stretching happen together, no slug is produced and no material leaves the sheet. The metal that would have been the hole is still there - it has become the strand beside the hole. The sheet therefore grows: a relatively small parent sheet yields a substantially larger finished panel.

The points where the knives do not cut become the junctions or bonds, and they remain continuous parent metal. Those junctions are the reason a cut expanded panel holds together, and the reason the panel distributes load across itself rather than through discrete members.

They are the four dimensions that define the mesh geometry, and a panel cannot be ordered without them.

SWD is the short way of the diamond, measured across the narrow axis of the opening from centre to centre of the bonds. LWD is the long way of the diamond, measured across the wide axis. Together they describe the opening's size and its proportions.

Strand width is the amount of metal fed into the machine on each stroke, which becomes the width of the material forming the sides of each diamond. Strand thickness is the thickness of that material - in standard expanded metal it is simply the parent sheet thickness, but in flattened material the rolling changes it, so the finished figure differs.

Orientation matters when you fit the panel. The SWD direction is the stiffer axis, so it should run across the span. Rotating a panel to make it fit an opening changes its structural behaviour.

One extra manufacturing step, and a set of trade-offs that follow from it.

Standard expanded metal comes straight off the expanding press. Its strands remain angled out of the plane of the sheet, so the surface is raised and textured, the panel is rigid, and it grips underfoot. Flattened expanded metal is taken from that same press and passed through a cold rolling mill, which presses the strands down into the plane of the sheet.

Flattening produces a smoother, flatter panel that sits neatly against a frame, looks more refined, and is easier to handle and to clean. It also lengthens the panel slightly and reduces the overall thickness. The cost is the extra operation, plus some loss of the rigidity that the raised strands provided.

Use standard where grip, rigidity and cost matter. Use flattened where flatness, appearance or a smooth surface matters.

Not structurally, which is one of its practical strengths. Because the panel is one continuous piece of parent metal with uncut junctions throughout, cutting it does not release anything - the remaining panel keeps working and the offcut is usable.

This is a genuine difference from welded bar grating, where cutting between cross rods leaves bearing bars untied and the panel must be banded before it can carry load again.

Edging is still worth fitting for safety and finish. A cut across expanded metal leaves a row of sharp strand ends that will catch hands, gloves and clothing, so any cut edge within reach should be trimmed or covered. On galvanised material the cut also exposes bare steel along every severed strand, which in a wet location needs treating. Cutting along a line of junctions rather than through the middle of strands gives a stronger and tidier edge.

The heavier grating grades are, and they are made specifically for it. The lighter sheet grades are not.

Expanded metal is produced across a wide range, from thin decorative and screening meshes through to substantial grating grades quoted by weight per unit area and supplied with published load tables. Those grating grades are used for catwalks, platforms, walkways and mezzanine infill, and the raised diamond of the standard form gives good multi-directional grip.

The light sheet grades are intended for guarding, screening, infill, ventilation and fencing, and they will deflect badly or fail under foot traffic.

Select from the grating range for any walking surface, work from the load table for the actual clear span and design load, and check deflection as well as strength. A panel that feels springy underfoot is treated as unsafe regardless of its calculated capacity.

Chosen on exposure, with particular attention to the cut edges the expanding process creates along every strand.

Self-colour carbon steel suits internal dry applications and panels that will be painted or powder coated as part of an assembly. Pre-galvanised sheet is economical, but expanding it cuts through the coating along every strand, leaving a very large total length of bare edge - it is not suitable for external use. Hot dip galvanising after expanding coats the strands and the cut edges together and is the standard external and industrial specification.

Stainless steel is used in food and pharmaceutical areas, coastal and chemical environments, and architectural applications where the panel is visible and must not stain.

The rule to remember is that pre-coated material and expanded metal are a poor combination outdoors, because the process itself destroys the coating exactly where the panel needs it.

Applications where an open surface is needed and strength per kilogram or cost per square metre matters more than a flat face or a precise aperture.

The largest groups are machine and conveyor guarding, walkway and catwalk flooring in the grating grades, mezzanine and balustrade infill, fencing and security screens, and ventilation panels in enclosures and plant rooms. It is also widely used as a plaster and render reinforcement lath, as a support layer in filtration, in shelving and storage, and as a lightweight stiffened panel wherever a thin sheet would be too floppy.

Architecturally the raised diamond gives a directional texture that changes with viewing angle and light, which is used deliberately in facades, screens and ceiling panels - usually in the flattened form where a cleaner face is wanted, and in stainless or galvanised finish for durability.