Steel grating is specified with a code like 19-W-4, and once you can read it the whole product range makes sense. That designation means bearing bars at 19/16 in centers, welded construction, cross bars at 4 in centers. This page explains the code, lists the standard bar sizes and spacings, covers the four construction types, and sets out what a complete specification has to say.
How to Read 19-W-4
| Part | Means |
|---|---|
| 19 | Bearing bar spacing, 19/16 in on center |
| W | Welded construction |
| 4 | Cross bar spacing, 4 in on center |
You will see the same product written as W-19-4 or 19-W-4; both are standard and both mean the same thing. The 19 is sixteenths, so 19/16 in is 1-3/16 in, the most common spacing in general industrial use.
What the designation does not tell you is the bearing bar size, and that is the part carrying the load. A 19-W-4 panel in 1 in by 1/8 in bar and one in 2-1/2 in by 3/16 in bar share a designation and have wildly different capacities. The bar size always has to be stated separately.
Standard Sizes
| Dimension | Standard options |
|---|---|
| Bearing bar spacing | 7/16, 1/2, 11/16, 15/16, 1-3/16 in on center |
| Bearing bar depth | 3/4, 1, 1-1/4, 1-1/2, 1-3/4, 2, 2-1/4, 2-1/2 in |
| Bearing bar thickness | 1/8, 3/16, 1/4, 3/8 in |
| Cross bar spacing | 2 or 4 in on center |
Depth is the lever you pull for capacity. Grating spans on its bearing bars, which act as a row of small beams, and bending capacity rises with the square of depth. Going from a 1 in bar to a 2 in bar at the same thickness roughly quadruples the section modulus, while only doubling the steel. Thickness, by contrast, buys capacity in direct proportion. Deeper is almost always the more efficient move, which is the same reasoning behind choosing a deeper I-beam over a heavier shallow one.
Tighter bearing bar spacing adds capacity too, since more bars share the load, and it is also what controls whether small objects, heels or tools fall through. The 7/16 and 1/2 in spacings exist mainly for that reason rather than for strength.
The Four Construction Types
| Type | How it is made | Typical use |
|---|---|---|
| Welded | Cross bars resistance-welded across the bearing bars | The general-purpose default, strongest and cheapest |
| Swage-locked | Cross bars pressed into punched holes and swaged tight | Aluminum, and where welding is unsuitable |
| Press-locked | Cross bars forced into notches under pressure | Architectural work, cleaner appearance |
| Riveted | Bars joined with rivets through the intersections | Heavy duty, high impact, long service |
Welded is the default for industrial steel and will be the right answer unless something specific rules it out. Aluminum is normally swage-locked, because the metallurgy makes resistance welding impractical.
Traffic Surface
Four options, and this is a safety decision rather than a finish preference: plain, serrated, knurled, or an applied abrasive finish consisting of aluminum-oxide aggregate in an epoxy-resin adhesive.
Plain is fine indoors and dry. Serrated notches the top edge of every bearing bar and is the normal choice anywhere there is oil, water, ice or a slope. Serration costs a little depth off the bar, so capacity drops slightly for the same nominal size, which the load tables account for. Applied abrasive finishes give the most grip and are used on stair treads and wet process areas.
The Standards Behind It
Grating is governed by the NAAMM Metal Bar Grating Manuals, MBG 531 and MBG 532. Between them they establish terminology and definitions, outline design requirements, specify tolerance limits, provide the load tables for different configurations, detail manufacturing processes and set quality control standards. The load tables in MBG 531 are derived from the design formulas and procedures in the companion engineering design manual, MBG 534.
That lineage matters when someone offers you a load table. A manufacturer’s table traceable to MBG 534 is a known quantity. An unattributed table from a catalog is not, and the two can differ on deflection limits, which is usually what governs a walkway rather than strength.
OSHA regulations also apply to anything people walk on: 29 CFR 1910 Subpart D covering walking-working surfaces, with 1910.22 for general requirements and 1910.25 for stairways, plus 29 CFR 1926.501 on the duty to have fall protection. These drive opening sizes, clearances and edge protection, and they are separate from whether the grating is strong enough.
What a Complete Specification Says
Seven items, and leaving any of them out means somebody else is choosing for you:
- Material: steel, stainless steel or aluminum
- Type: welded, press-locked, swage-locked or riveted
- Bearing bar spacing
- Bearing bar size, chosen from the service load and the clear span
- Traffic surface: plain, serrated, knurled or applied abrasive
- Banding or other trim at cut edges and openings
- Finish: mill, galvanized, painted, anodized or powder-coated
Shop drawings should then show the plans and panel layouts, span directions, bearing bar sizes and spacings, banding, cutouts, support framing, clips and anchors, any hinge or lift hardware, and the finishes.
Two of those are quietly expensive to get wrong. Span direction must be on the drawing, because grating has almost no capacity across the cross bars; laying a panel the wrong way round is a genuine hazard rather than an inefficiency. And banding is needed wherever a panel is cut, including around pipe penetrations, since an unbanded cut leaves bearing bars unsupported at the free end and a row of sharp edges.
On finish: a shop primer protects gratings in transit only and is not a service coating. For anything outdoors or wet, hot-dip galvanizing after fabrication is the normal answer, for the same reason set out in does galvanized steel rust. Where grating sits on steel framing, check the support itself as well, whether that is open web joists or rolled beams.
Steel Grating FAQ
What does 19-W-4 mean?
Bearing bars at 19/16 in on center, welded construction, cross bars at 4 in on center. It says nothing about bearing bar size, which is specified separately and is what determines load capacity.
What is the difference between 19-W-4 and 19-SP-4?
The middle letters give the construction. W is welded; SP indicates a swage-locked or press-locked product depending on the manufacturer’s convention. Same geometry, different method of joining the cross bars, and different load tables.
How far can steel grating span?
It depends on the bearing bar size, the spacing, the load and the deflection limit, so it has to come from a load table for the exact product. Deflection usually governs before strength on a walkway, because a floor that feels springy fails its users long before it fails structurally.
Does serration reduce capacity?
Slightly, since notching removes material from the top of the bearing bar where bending stress is highest. Manufacturers publish separate tables for serrated product; use those rather than derating the plain figures yourself.
Sources: Los Alamos National Laboratory Engineering Standards, Specification Section 05 5313, Metal Bar Gratings, for the 19-W-4 and W-19-4 designation, the bearing bar spacing, depth and thickness options, cross bar spacings, traffic surface options, construction types, the specification and shop drawing checklists, the shop primer note, and the NAAMM MBG 531, MBG 532 and MBG 534 and OSHA 29 CFR references. Last updated: October 2026.
This page is reference information only and is not engineering advice. Walking surfaces are life-safety elements; size grating from the manufacturer’s load tables for the exact product and have the design checked. Full disclaimer.