Corner radius is a functional dimension of stainless steel square and rectangular tube. It affects usable flat-face width, bracket fit, miter joints, base plates and laser-cut features. Specify the governing standard, wall thickness, outside size and any project-specific radius limit, then inspect each relevant corner with an agreed method.
Why Corner Radius Matters
Square tube is formed with rounded corners; the nominal width and height do not describe the entire section profile. A larger radius reduces the flat contact area and can interfere with close-fitting brackets, clamps, plates and machined features. Variation among corners can also affect weld gaps and cosmetic alignment.
Four dimensions that work together
- Outside width and height: the overall envelope across the faces.
- Wall thickness: influences the achievable inside and outside corner profile.
- Outside corner radius: the external curved portion between adjacent faces.
- Flat-face width: the usable straight portion between tangent points.
What ASTM A554 Covers
ASTM A554 covers welded stainless mechanical tubing in round, square, rectangular and special shapes for applications where appearance, mechanical properties or corrosion resistance is needed. The standard includes dimensional requirements for square and rectangular tubing, including the method used to assess corner radii. The purchase order must still identify the grade, dimensions, condition, finish and any optional or tighter requirements.
How to Specify Corner Radius in an RFQ
| RFQ item | What to state | Why |
|---|---|---|
| Product standard | Standard number and edition | Defines the baseline dimensional rules. |
| Section size | Outside width × height × nominal wall | Links the corner profile to the actual section. |
| Radius requirement | Standard maximum or agreed project limit | Prevents fit-up disputes. |
| Critical interface | Bracket, base plate, miter, clamp or laser feature | Explains where the radius matters. |
| Inspection method | Radius gauge, template, optical method or agreed drawing check | Makes acceptance repeatable. |
| Sampling plan | Number of pieces, locations and corners | Defines how a lot will be accepted. |
Practical Inspection Sequence
- Verify the material identity, standard, size and wall against the order.
- Confirm the tube is clean and free from burrs or damage that would disturb the gauge.
- Measure width, height and wall at the specified locations.
- Check each required corner with the agreed radius gauge or profile method.
- Record the largest radius and identify the measurement location.
- Check twist, straightness and face concavity/convexity when they affect fit-up.
- Trial-fit the actual mating component if the assembly has a critical interface.
Common Purchasing Mistakes
- Specifying only “50 × 50 × 2 mm” without a product standard.
- Assuming all four corners or all production routes produce an identical radius.
- Using a carbon-steel structural-tube rule for stainless mechanical tubing without approval.
- Measuring over a weld, burr, dent or polished transition without an agreed datum.
- Setting an unnecessarily sharp radius that raises cost or is not manufacturable.
Questions and Answers
Is the inside radius the same as the outside radius?
No. Wall thickness and forming influence the relationship. State which radius controls the assembly.
Does a polished finish change the radius?
Polishing can alter the local surface profile if aggressive material removal is used. Critical cosmetic or fit surfaces should be identified before finishing.
Can the buyer request a tighter radius?
A special limit may be agreed with the producer, but it should be reviewed for section size, wall, grade, forming route, tooling and quantity before it becomes an acceptance requirement.
Prepare a Complete Square-Tube RFQ
Send the grade, standard, width × height × wall × length, condition, finish, corner-radius requirement, tolerances, critical interface, quantity, inspection documents and destination.
Contact SAKY STEEL with your drawing and acceptance requirements
Post time: Nov-03-2026