Metal buying guides / Materials
How to Specify Square Steel Tube Dimensions
A square tube description needs its outside size, nominal wall thickness, grade, finished length, and quantity. Keep those fields separate. A 2-inch square section is not a promise of a 2-inch clear opening inside it.
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Quick answer
Square tube is normally described by its outside width and height, wall thickness, grade and cut length. A 2 × 2-inch tube has a nominal outside size of 2 inches. Its inside opening is smaller, and rounded corners or an internal weld seam can prevent another piece from sliding in.
Wall thickness is the thickness of the metal around the hollow opening. “Nominal” means the listed size; the actual thickness can vary within the material specification.
For example, “A500 Grade B, 2 x 2 x .120-inch wall, ten pieces at 24 inches” describes ten separate lengths of one tube section.
What the numbers mean
On a small screen, scroll the table sideways to see every column.
| Part of the description | What it identifies |
|---|---|
| A500 Grade B | Material specification and grade |
| 2 x 2 inches | Outside width and height |
| .120-inch wall | Nominal wall thickness |
| 24 inches | Finished cut length of each piece |
| Quantity 10 | Ten separate pieces |
For rectangular tube, outside width and height differ. Label the dimensions instead of relying on the reader to infer which number is the length.
Why the inside opening needs a separate check
Subtracting twice the nominal wall from the outside size gives a simplified opening estimate. For a 2-inch section with .120-inch walls, that arithmetic gives 1.760 inches. It does not establish a usable square clearance of that size.
Actual dimensions, rounded internal corners, and a weld seam can affect the fit. The Steel Tube Institute explains how an internal seam can interfere with a fitted plate. If another part must slide inside, specify and verify the actual fit rather than approving it from the subtraction alone.
Take particular care with a telescoping assembly. Sliding clearance, alignment, coatings, and the inserted part's corners all matter. An outside-size match is only the beginning of the check.
Separate straight ends from angled ends
A straight cut length is straightforward to describe. For a miter, which is an angled end cut, include a sketch showing the angle direction, the face viewed, and whether length is measured between long points, short points, or another reference.
Two ends cut at the same angle can face the same direction or opposite directions. Those pieces can have very different uses. Draw both ends instead of writing only “45 degrees each end.”
For standard straight cuts, enter the finished length without adding saw kerf. For miters, holes, slots, or assembly work, use the custom request.
Keep cut tolerance separate from tube dimensions
Rapid Metals' published standard finished cut tolerance is ±1/16 inch. That applies to the length being cut. It does not specify the outside section, wall tolerance, inside clearance, or the capacity of a frame.
If the length is a close-fit dimension, put the allowable range in the request before ordering. Our cut-tolerance guide walks through that distinction.
For a specified structural or machine application, retain the required grade and documentation. This buying guide does not select tube wall for a load-bearing design.
Ready to check a straightforward order? Configure ten 24-inch lengths of the listed A500 Grade B section and review the current price and order details.