Expanded metal gets specified like this:
1/2″ #16 – Flattened Expanded Metal – 48″ x 96″ Sheet
Two numbers, and neither one is the size of the hole. This is the third article in our series on reading mesh specifications — we have already covered mesh count vs. inches and perforated hole-on-centre specs — and expanded metal is the most cryptic of the three.
The First Number: The Diamond, Not The Hole
Expanded metal is made by slitting a solid sheet and stretching it, which pulls the slits open into a pattern of diamonds. The 1/2″ in the spec is the nominal size of that diamond measured the short way — in the trade, the short way of design (SWD) — and by convention it is measured centre-to-centre across the diamond, not across the clear space.
Because the metal strands themselves take up part of that distance, the clear opening you could actually pass something through is smaller than the number on the label. If you are screening to keep something specific in or out — a rodent, a fastener, a finger — the honest way to buy is to tell us what has to fit through (or not fit through) and let us measure the material, or just get a free sample and check it against the real thing.
If that sounds familiar, it is the same trap as woven mesh, where “1/4 inch” hardware cloth has a 0.224″ opening. Nominal names describe the pattern, not the hole.
The Second Number: Sheet Gauge — And Lower Means Thicker
The #16 is the gauge of the steel sheet the pattern was expanded from. Gauge numbers run backwards, the same way wire gauge does: the lower the number, the thicker the metal.
Our stocked range runs from #9 — the heavy end, what you would put under foot traffic — down to #20, a light sheet for trim, guards and decorative work:
- #9 — heavy: walkways, ramps, security barriers, anything structural
- #13 — medium: machine guards, heavy grilles, racks
- #16 — the everyday weight: guards, grilles, enclosures, infill panels
- #18–#20 — light: vents, speaker grilles, cabinet panels, decorative work
Aluminum and copper skip the gauge system entirely and are specified by decimal thickness — our 1/2″ aluminum comes in .051″, .081″ and .125″ stock, and our copper in .016″. Same idea, plainer units.
The Number That Is Not On The Label
Diamonds are not square. Every expanded pattern also has a long way of design (LWD), typically about twice the short way — a 1/2″ diamond is roughly an inch long the other direction.
That matters twice. Visually, the diamonds have a direction, and two panels installed with the pattern running different ways will read as mismatched even though they are the same material. Structurally, the strands run with the long way, so the sheet behaves differently across its two axes. If your panel has a critical span or a pattern direction that matters, say so on the quote and we will cut accordingly.
Flattened vs. Raised
As it comes off the expander, the strands sit at an angle — the sheet has texture and extra depth. That is standard (raised) expanded metal, and the grip underfoot is exactly why walkway treads use it. The cover photo above is raised material on a building facade — you can see the strands catching the light at an angle.
Run that sheet through a cold roll and the strands lie down flat: flattened expanded metal — smooth-faced, slightly thinner and wider than it started, easier to fabricate and cleaner-looking in a panel or guard.
Everything in our stocked range is flattened. If a job genuinely needs raised material — usually for traction — treat it as a quote item and ask us.
Why One Piece Of Metal Matters
Because expanded metal is slit and stretched from a single solid sheet, there are no welds, no woven joints, and no crimps anywhere in it. Nothing can loosen, unravel, or pop a weld under a hit — if you cut it, the edge stays put. That is why security screens, lockers, cages and machine guards default to expanded metal, and it is also why it is economical: the process wastes no material, and one sheet of steel becomes up to several times its own area of mesh.
For guarding specifically, the opening rules come from the standard that governs the machine, not from preference — see machine guard opening sizes.
What We Stock
All flattened, all cut to your dimensions in Hayward. Representative items — the full collection is here:
| Diamond | Weights stocked | Materials |
|---|---|---|
| 1/4″ | #18, #20 | Plain steel, 304 stainless, copper (.016″) |
| 1/2″ | #13, #16, #18, #20 | Plain steel, galvanized, 304, 316, 316L, aluminum (.051″–.081″) |
| 3/4″ | #9, #13, #16 | Plain steel, galvanized, 304, 316, aluminum (.081″–.125″) |
| 1″ | #16 | Plain steel |
| 1-1/2″ | #9, #13, #16 | Plain steel, 304, aluminum |
Frequently Asked Questions
Is the 1/2″ the size of the opening?
No — it is the nominal diamond designation, measured the short way, centre-to-centre. The clear opening is smaller. If the opening size is critical, ask for a sample and measure it.
What does #9 vs. #16 mean?
The gauge of the sheet before expanding. Lower number = thicker metal: #9 is walkway-heavy, #16 is everyday guard weight, #20 is light trim stock.
Is expanded metal stronger than welded mesh?
They fail differently. Expanded metal has no joints to fail and holds its geometry when struck; welded mesh gives you exact square openings. For guards, welded and expanded both work — see expanded vs. perforated for how it compares on the sheet side.
Can you cut it to size?
Yes — every sheet we sell is cut to your dimensions, and we fabricate panels, guards and edged pieces from it.
Do you stock raised (standard) expanded metal?
Our stocked range is flattened. Raised material for traction work is a quote item.
Tell Us The Job
If you know the spec, send it. If you only know the job — a guard for this machine, a screen over this window, a tread for this ramp — tell us that instead, and we will spec it with you.
Request a quote, order a free sample, or call (510) 887-8787.
Cover photo: expanded metal facade by APovlsen, via Wikimedia Commons, licensed CC BY-SA 4.0; cropped.