Filter support mesh technical guide
Terminology, formulas and a specification checklist for filter engineers and buyers working with expanded metal, welded mesh and epoxy coated screen.
Expanded metal: reading a specification
One "4 x 8" can describe several different meshes. A complete expanded metal specification states the material, the thickness (plate or overall mesh), SWD x LWD (pitch or clear opening), strand width, whether the mesh is flattened, and which direction the long way of the diamond runs on the roll. Our tables list SWD first; many buyers write LWD first.
Open area and weight of expanded metal
For a quick estimate:
- Strip weight (g/m²) = thickness (mm) x density (g/cm³) x 1,000
- Area weight (g/m²) ≈ strip weight x 2 x strand width / SWD
- Calculated open area ≈ 1 - 2 x strand width / SWD
Worked example: 304 stainless, 0.40 mm thick, 0.51 mm strand, SWD 4 mm. Strip weight = 0.40 x 7.93 x 1,000 = 3,172 g/m². Area weight ≈ 3,172 x 2 x 0.51 / 4 ≈ 809 g/m². Calculated open area ≈ 1 - 2 x 0.51 / 4 ≈ 75%.
Measured (projected) open area can differ from the calculated figure, so always ask which one a supplier is quoting. Roll weight = area weight x width x length, which makes the weight of one full roll a reliable way to match an existing mesh.
Welded and woven mesh: open area
For a square mesh with pitch p and wire diameter d, open area = ((p - d) / p)². Example: 1 x 1 in welded mesh (25.4 mm pitch) with 0.81 mm wire has about 94% open area. For woven epoxy screen, use the bare and the coated wire diameter separately: the coating reduces open area.
Wire size: gauge numbers are not specifications
The same gauge number means different wire diameters in the US, UK and AWG systems. State wire diameter in millimetres or decimal inches on every drawing and purchase order, and treat the gauge number as a note.
Request-for-quote checklist
- Filter type and where the mesh sits: pleat support, core, outer wrap or backing grid
- Material and coating, with the coating class if you have one
- Thickness or wire diameter, and whether it is measured before or after coating
- Opening: SWD x LWD for expanded metal, mesh count or pitch for woven and welded mesh
- Strand width and flattened or raised (expanded metal)
- Roll widths, quantities per width and roll length
- Core inner diameter, maximum roll diameter and roll weight your unwinder accepts
- Annual volume, order size and destination
- Current roll weight, a sample or a drawing if you are replacing an existing mesh
Further reading
- Galvanized before vs after welding
- Epoxy mesh: bare vs coated wire diameter
- Selection guide: expanded vs epoxy vs welded vs PP
Related support media
Frequently asked questions
What is the difference between SWD and SWO?
SWD is the short way of the diamond measured centre to centre; SWO is the clear opening inside the diamond, which is always smaller.
Why does my supplier's thickness not match my measurement?
Data sheets sometimes give the plate thickness before expanding and sometimes the overall thickness of raised mesh, which is greater. Always state which one you mean.
How do I convert roll length to weight?
Roll weight = area weight x width x length. For expanded metal, area weight is approximately strip weight x 2 x strand width / SWD.
Send your specification
We check that the numbers are consistent, propose a matching mesh and send samples.