1-inch steel tubing is round, square, or rectangular steel tube with a 1.000-inch outside diameter, sized by actual OD and wall thickness rather than by nominal pipe size.
Two specs cover almost everything sold in that size, and a pile of mystery-steel problems traces back to choosing the wrong one. Mechanical tubing runs on ASTM A513; structural tubing runs on ASTM A500. A 1-inch tube that meets one spec will not match the other on tolerance, yield strength, or fit-up.
This is a tubing size, not a tubing standard. Manufacturers sort 1-inch tube by outside dimension, wall thickness, material grade, and the ASTM spec it was produced under, and those four variables matter more than the number itself.
Tubing Or Pipe? Why The 1-Inch Label Means Something Different
That single distinction wrecks more projects than any other mix-up.
Gray iron and steel pipe carries a nominal size that rarely equals its true OD, so 1-inch pipe measures noticeably larger than 1 inch across. Wall thickness is a separate number on top of it, which is why “1-inch tubing” alone never tells you how strong or how heavy the piece is.
Order by the wrong system and you lose the money on the cut, not the purchase. Threaded fittings, couplings, and hangers built for pipe won’t seat on tube of the same nominal size, and tube fittings won’t grip pipe.
The Two ASTM Specs That Cover Most 1-Inch Tubing
ASTM A513 governs mechanical tubing and ASTM A500 governs structural tubing, and the spec is the first thing to check on any cut list. Each one sets its own chemistry, tolerance, and testing requirements.
- ASTM A513 (mechanical tubing). Low-carbon steel, commonly SAE 1020 or 1026, produced as electric-resistance-welded (ERW) tube in either as-welded or DOM form. Round A513 tubing is listed from 3/4 inch to 2 inch OD, which puts 1 inch squarely in range. ERW round tubing runs from 1 inch to 3.5 inch OD with walls from.035 inch to.250 inch.
- ASTM A500 (structural tubing). Cold-formed carbon steel hollow structural section (HSS), welded or seamless. HSS is capped at a total perimeter of 88 inches, with domestic round sizes reaching 28 inches OD and wall thicknesses up to 1-inch nominal.
- Galvanized options. ASTM A787 and ASTM A1076 cover galvanized mechanical and structural tubing when corrosion resistance matters.
Common finishes follow the spec: mill, galvanized, painted, or cold-rolled and pickled, depending on how the tube was processed after forming.
Tolerance, Or Where The Two Specs Quietly Diverge
The gap opens up in structural design rather than in the raw number. The Steel Tube Institute notes that AISC 360-16 Section B4.2 uses 0.93 times nominal thickness in calculations involving thickness, a built-in allowance for how much a formed wall can vary. Ignore that factor on a loaded member and the math looks fine on paper while the steel doesn’t match it.
You can see the practical difference below. Both columns apply to 1-inch OD round tube, and the spec you’re buying is what changes between them.
| Attribute | ASTM A513 Mechanical | ASTM A500 Structural |
|---|---|---|
| Core material | Low-carbon steel (SAE 1020/1026 typical) | Cold-formed carbon steel HSS |
| OD tolerance at 1 inch | ±0.005 inch | ±0.5% of OD (0.005 inch) |
| Wall tolerance | ±10% of nominal | ±10% of nominal |
| Forming method | ERW, as-welded or DOM | Welded or seamless, cold-formed |
| Size range listed | 3/4 to 2 inch OD (round A513) | HSS up to 88-inch total perimeter |
| Design allowance | Not specified for structural loads | 0.93 × nominal thickness (AISC 360-16 B4.2) |
| Typical use | Machinery, conveyors, OEM parts | Columns, supports, building frames |
What 1-Inch Tubing Actually Gets Used For
Mechanical tubing lands in automotive components, OEM parts, conveyors, machinery, and general fabrication. Structural tubing carries load in columns, supports, building frames, and equipment supports.
Square and rectangular 1-inch tubing is the familiar sight in frames, shelving, racks, and supports. Round tube takes bending and rolling better; square gives you flat faces that bolt cleanly to a plate or bracket. That’s often the deciding factor before any spec question comes up.
Both specs are widely stocked in cut lengths and full sticks, and retail pricing is inconsistent and product-specific — you’ll see 1-inch carbon steel square tubing listed anywhere from the high twenties to the high forties depending on gauge and SKU, and round mechanical tube from around $20 upward. Comparing several suppliers side by side is the only way to know what a given cut actually costs. If you’re shopping for a specific project, this roundup of tested 1-inch steel tubing options covers gauges and buying criteria in one place.
Before You Cut Or Weld: Specs You Have To Check
The spec decides the job, and mixing A500 and A513 without checking grade, yield, and tolerance is how fit-up and strength problems start.
The Steel Tube Institute publishes the ASTM A500 specification details if you need the source document on thickness allowances and HSS limits.
Match the material to the load and the environment. A support column in a wet shop needs the galvanized route; an interior machine guard doesn’t. Check that the wall thickness in the catalog matches the one in your calculation, and remember that 1-inch OD square tube and 1-inch OD round tube handle stress differently even at identical wall.
FAQs
Is 1-inch tubing the same as 1-inch pipe?
No. Pipe is sized by nominal bore, so 1-inch pipe measures larger than 1.000 inch across the outside. The two use different fittings and are not interchangeable in threaded assemblies or hanger systems.
Which spec should I pick, A513 or A500?
Pick A500 for anything carrying structural load, such as columns, frames, and equipment supports. Pick A513 for mechanical and fabrication work, including conveyors, machinery, and OEM parts. The two have different tolerances and design allowances, so check grade, yield, and thickness before substituting one for the other.
Does wall thickness change with the spec at 1 inch?
AISC 360-16 Section B4.2 calls for using 0.93 times nominal thickness in calculations involving thickness, so a structural member is designed thinner than its label suggests. Confirm actual wall before you weld or load it.
References & Sources
- Steel Tube Institute. “ASTM A500” Supports HSS perimeter and wall limits and the AISC 360-16 thickness factor.
- T&B Tube. “ASTM Standards” Covers the ASTM A513, A500, A787, and A1076 tubing standards.
- US Tubes. “ASTM A513 Specification and Performance” Source for A513 ERW and DOM forms and size ranges.
