SWM, LWM, Strand Width and Open Area: How to Read Expanded Metal Drawings Correctly

Expanded metal is made from a solid sheet that is slit and stretched. The cuts open into diamond-shaped apertures, while the metal left between the openings becomes the strand. The process sounds simple, but the drawing language can create expensive confusion when different suppliers use different conventions.

A customer we will call Emma sent a sketch marked “50 × 25 mesh, 3 mm thick.” One supplier treated 50 mm as the long way of mesh, another treated it as the short way, and a third assumed 3 mm was the strand thickness after flattening. The quotations looked comparable, but the products were not.

We helped her turn the sketch into a controlled specification: SWM, LWM, strand width, original sheet thickness, raised or flattened condition, panel size, orientation, open area target, edge condition, and tolerance. Once these were fixed, the weight, appearance, stiffness, and price could be compared on the same basis.

Real pain: buyers think the same mesh code always means the same product. Counter-intuitive point: two sheets with similar diamond openings can perform very differently because strand width and thickness change the remaining metal. Industry explanation: expanded metal is directional and its geometry is linked; changing one parameter affects several outcomes at once. Memorable conclusion: define the strand, not only the hole. Action direction: place all core dimensions and the mesh orientation on the approved drawing before production.

1. SWM: Short Way of Mesh

SWM means short way of mesh. It is the shorter diamond dimension, usually measured from the centre of one bond to the centre of the next equivalent bond. It strongly influences aperture size, open area, and the visual density of the mesh.

A larger SWM generally creates larger openings and higher airflow, but may reduce stiffness if strand geometry and thickness remain unchanged. A smaller SWM usually creates a tighter pattern, improved screening, and more metal per unit area.

2. LWM: Long Way of Mesh

LWM means long way of mesh. It is the longer diamond dimension and defines the direction in which the sheet was expanded. Because expanded metal is directional, LWM orientation should be shown in relation to the finished panel and supports.

For many walkway and catwalk arrangements, placing the long way of the diamond across the supported span can improve stiffness. The project engineer should confirm the final arrangement for the selected mesh and load case.

3. Strand Width

Strand width describes the width of metal left between apertures. A wider strand usually increases weight, stiffness, opacity, and impact resistance while reducing open area. A narrow strand can improve transparency and reduce weight but may be more sensitive to handling damage or deflection.

Strand width is especially important for machine guards, facade screens, and architectural panels where the customer is balancing visibility with screening. It should not be guessed from a photograph.

4. Strand Thickness

Strand thickness is normally related to the thickness of the original sheet before expanding. For raised mesh, the finished overall height can be greater than the original sheet thickness because the strands sit at an angle. For flattened mesh, rolling changes the profile and may change the final gauge or width slightly.

Always state whether the thickness refers to the original sheet, strand metal, or finished overall mesh height. This prevents confusion during inspection.

5. Aperture and Open Area

The aperture is the clear opening between strands. Open area is the percentage of void compared with the total sheet area. It affects airflow, drainage, light transmission, visibility, debris control, and acoustic transparency.

Open area is not a stand-alone performance guarantee. A high-open-area sheet can still be unsuitable if it lacks required stiffness, allows unsafe reach, or fails to control the debris size. A low-open-area sheet can block airflow or create unwanted wind loading on a facade.

6. Bonds and the Expanded Pattern

The bond is the intersection where strands meet. Bond width, bond length, and pattern regularity influence appearance and load transfer. In architectural work, inconsistent bonds are visually obvious across large facades. In industrial work, distorted bonds can create local weakness or poor fitting at frames.

Our factory inspection checks pattern repeat, SWM, LWM, strand width, thickness, panel size, squareness, flatness, and visible damage. Where a project needs a reference sample, production is compared with the approved sample rather than relying only on a verbal mesh name.

7. How One Change Affects the Whole Product

These are typical relationships, not a substitute for project-specific engineering or testing.

8. The Drawing Checklist We Use

• Material and grade
• Raised or flattened condition
• SWM and LWM
• Strand width and original sheet thickness
• Finished panel size and LWM direction
• Target open area or aperture requirement
• Flatness, squareness, and dimensional tolerances
• Cut-edge condition, banding, frames, folds, and fixing holes
• Finish, colour, coating system, and repair method
• Panel marks, packing sequence, and sample approval

Our working style is to mark unclear dimensions before quoting. This may add one drawing review step, but it prevents a full batch from being manufactured to the wrong interpretation. We also avoid changing a mesh code silently when raw material or machine limits require an adjustment; the customer receives the revised geometry for approval.

9. Common Questions

Can open area alone identify the mesh?
No. Different combinations of SWM, LWM, strand width, and thickness can produce similar open-area percentages.

Can I compare quotations by kilograms per square metre?
Weight is useful, but it does not confirm opening geometry, orientation, flatness, edge quality, or finish.

Should I specify aperture size or SWM/LWM?
For controlled manufacturing, include SWM and LWM and state any minimum clear aperture requirement separately.

Why does the flattened sheet look wider?
Rolling can change the geometry and final dimensions. Confirm the supplier’s finished-size basis.

Once the drawing is correct, the next step is checking how the selected sheet fits into walkway, platform, and machine-guard safety requirements.

This article helps you solve the pain of comparing non-equivalent quotations and gives you the benefit of fewer drawing errors, more accurate pricing, and a mesh that arrives with the expected opening, weight, orientation, and finish.

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