Sooner or later, anyone building a machine guard out of mesh asks the same question: how big can the openings be?
Search it and you will land on OSHA Table O-10. It is a real table in a real federal regulation, and the logic behind it is sound: the further a guard sits from the hazard, the larger its openings may be, because a finger reaching through a small hole cannot travel far enough to touch anything.
It is also written for one narrow class of machine — which is the part almost nobody mentions.
Table O-10, As Written
From 29 CFR 1910.217. All measurements in inches.
| Distance of opening from point of operation | Maximum width of opening |
|---|---|
| ½ to 1½ | ¼ |
| 1½ to 2½ | ⅜ |
| 2½ to 3½ | ½ |
| 3½ to 5½ | ⅝ |
| 5½ to 6½ | ¾ |
| 6½ to 7½ | ⅞ |
| 7½ to 12½ | 1¼ |
| 12½ to 15½ | 1½ |
| 15½ to 17½ | 1⅞ |
| 17½ to 31½ | 2⅛ |
Read it as a pair. A guard sitting half an inch off the hazard may have openings no wider than a quarter inch. Push the guard back to seven inches and you can go to nearly an inch. The trade is always distance against opening size.
The Part That Gets Skipped
Table O-10 lives inside 1910.217, which governs mechanical power presses. That standard explicitly excludes press brakes, hydraulic and pneumatic power presses, bulldozers, hot bending and hot metal presses, forging presses and hammers, and riveting machines.
So if you are guarding a conveyor, a mixer, a hydraulic press, a robot cell, or a fan, Table O-10 is not the rule that applies to you. It gets cited that way constantly, including by people selling guarding material.
What does apply generally is 1910.212, the general machine guarding standard. It requires that guards protect the operator and others from hazards such as point of operation, ingoing nip points, rotating parts, and flying chips or sparks — and it specifies no opening dimensions whatsoever. No table, no maximum, no distance formula.
That gap is deliberate. OSHA sets the duty; the engineering detail is left to consensus standards.
Where The General Numbers Come From
For guards outside the power-press world, the references practitioners actually use are ANSI B11.19 (safeguarding performance criteria) and ISO 13857 (safety distances for reaching over and through). Both are more sophisticated than Table O-10 in one important respect: the required distance depends on the shape of the opening, not just its size — a slot, a square, and a round hole of the same nominal dimension get different treatment, because a slot admits a finger differently than a round hole does.
Those are copyrighted consensus standards, so we are not going to reproduce their tables here, and you should not be working from a blog post anyway. If your guard is not on a mechanical power press, get the current edition of B11.19 or ISO 13857 in front of whoever signs off on the installation.
This article is background on mesh openings. It is not a compliance determination, and we are not safety engineers. The distance from the hazard, the reach path, and the standard that governs your specific machine are decisions for a qualified safety professional and your own risk assessment.
Mesh Openings Against The Table
With that said — here is how common stocked openings line up with the Table O-10 bands, if you are working on a press and want a starting point:
| Opening | O-10 band it satisfies | Typical material |
|---|---|---|
| ¼″ | ½″ and beyond — the closest mounting allowed | 4 mesh hardware cloth, 1/4″ perforated |
| ⅜″ | 1½″ and beyond | 3/8″ perforated steel |
| ½″ | 2½″ and beyond | 1/2″ welded mesh, 1/2″ perforated |
| ¾″ | 5½″ and beyond | 3/4″ hardware cloth |
| ½″ × 1″ | governed by the wider dimension — treat as 1″ | 1/2″ x 1″ welded |
Three things that trip people up when they measure:
- Measure the clear opening, not the nominal size. A mesh sold as 1/4″ may have a clear opening nearer 0.224″ once the wire is accounted for — that works in your favour here, but you should know the real number. See how mesh count works.
- A rectangular opening is governed by its wider dimension. A 1/2″ × 2″ welded mesh is a 2″ opening for this purpose, not a 1/2″ one.
- Every opening counts, not just the mesh. Gaps at the frame, slots for feed stock, and the space around an access panel are all openings. A perfectly specified panel in a frame with a 1″ gap at the bottom has a 1″ opening.
Rigidity Matters As Much As Opening
An opening only stays the size you specified if the panel does not deflect. Guarding is one of the few applications where welded mesh is usually the right answer over woven — the welds hold the geometry under a knock, where woven mesh can distort and open up locally. Heavier perforated sheet does the same job with a solid-panel look.
If a guard also has to contain something — a thrown fragment, a broken tool — opening size is no longer the governing question and you should be talking to us about wire diameter and panel thickness, not just mesh size.
Frequently Asked Questions
Does OSHA give a maximum opening for machine guards generally?
No. 1910.212 sets the requirement to guard but contains no opening dimensions. Table O-10 in 1910.217 does give dimensions, but only for mechanical power presses.
Is 1/2″ welded mesh acceptable for a machine guard?
It depends entirely on how far the guard sits from the hazard and which standard governs the machine. Under Table O-10, a 1/2″ opening needs at least 2½″ of clearance. Confirm against the standard that applies to you.
Woven or welded for guarding?
Usually welded, for rigidity. See welded vs. woven.
Can you supply guard panels finished, not just material?
We cut to size and fabricate — edging, framing, and panels. Send a drawing.
Send Us The Drawing
Tell us the opening you need and the panel size, and we will cut it. If you are still working out the opening, tell us the machine and the mounting distance and we will tell you what we would quote — then have your safety professional confirm it before you build.
More on this at wire mesh for machine guarding. Or request a quote and call (510) 887-8787.
General information about mesh openings, not a safety or compliance determination. Requirements depend on the machine, the governing standard, and your risk assessment. Consult a qualified safety professional.