Round, square and rectangular tube can be ordered from a size table. A special-shaped tube cannot. There is no catalogue size to point to, and the standards publish no tolerance table for the shape. Everything the mill needs has to come from your enquiry: the drawing, the profile, the forming process, the tolerances, the grade, the finish, the tooling and sample approval, and the inspection. This checklist explains each item and what to write.
1. Start with a dimensioned drawing
A special-shaped tube is quoted from the drawing, so the drawing has to carry all of the information. Send a DXF, DWG or STEP file, or a clear PDF, showing:
- the outer contour with all widths, heights and angles;
- the wall thickness, and whether it must be uniform around the section;
- corner radii, inside or outside, and which of the two is controlled;
- the critical dimensions: the ones that mate with other parts, such as a glass slot, a clamp face or a telescoping fit;
- a datum for measurement, for example the flat base of a D-shape.
Why this matters under ASTM A554. ASTM A554, the common specification for welded stainless mechanical tubing, covers round, square, rectangular and “special” shapes (Section 1.3). For special shapes, it only says the dimensions are “to be specified” by the purchaser (Section 4.1.4.3). Its tolerance tables cover round tubing (Tables 2 and 3) and square and rectangular tubing (Table 5) only. Straightness for special requirements is “agreed upon between the purchaser and producer” (Section 9.4). In other words, for a special shape the tolerances are whatever your drawing and order say. If they are missing, there is nothing to hold the supplier to.
2. Identify the profile family
Most shaped tubes fall into a few families. Naming yours helps the mill check for an existing die (see section 7).
| Profile | Typical size envelope | Wall | Typical uses |
|---|---|---|---|
| Oval and flat oval | Major 15–200 mm, minor 10–100 mm | 0.6–4.0 mm | Balustrades, handrails, furniture, automotive parts |
| D-shaped | Base 12–150 mm, height 8–80 mm | 0.8–5.0 mm | Wall rails, frames, guides |
| Triangular | Side 15–120 mm | 0.8–3.5 mm | Trusses, frames, architectural features |
| Hexagonal and octagonal | 10–100 mm across flats | 1.0–5.0 mm | Drive shafts, torque sleeves, tool handles |
| Grooved or slotted rail | OD 38.1–76.2 mm, slot 14–26 mm | 1.2–2.5 mm | Frameless glass balustrades, showcase rails |
| Custom profile | Envelope up to 200 mm | 0.5–5.0 mm | Machinery tracks, transit interiors, heat dissipation |
The size ranges are TeCarve’s current supply envelope. Larger sections can be reviewed on request.
3. Choose the forming process
Shaped tubes are made in two main ways. The process sets the tolerance you can expect and the cost.
| Roll forming (welded) | Cold drawing over a shaped mandrel | |
|---|---|---|
| How it works | Strip is formed through a series of contour rolls, welded, then sized | A round mother tube is drawn through a shaped die over a shaped mandrel |
| Typical tolerance | about ±0.20–0.40 mm | about ±0.08–0.15 mm |
| Wall around the section | Follows the strip; corners may thin slightly | More uniform around complex shapes |
| Surface | Good; weld seam present | Smooth inside and out |
| Best for | Medium to high volumes, architectural and structural profiles | Precision fits, telescoping parts, mechanisms |
If your part only needs to look right and fit a bracket, roll forming is usually the economical choice. If it must slide inside another tube or hold a precise fit, ask for cold drawing.
4. Specify every tolerance, not just the size
A shaped tube can be the right size and still fail to fit, because it is twisted, bowed or out of square. State each of these on the drawing or in the order:
- Dimensional tolerance on each critical dimension.
- Wall thickness tolerance. ±10% of the specified wall is the figure ASTM A554 applies to round, square and rectangular tubing, and is a sensible starting point.
- Corner radii. For square and rectangular tubing, A554 Table 5 sets maximum corner radii, measured as the effective corner radius (Fig. 1). For shaped tubes, put the radius and its tolerance on the drawing.
- Twist. Ask for a maximum in mm per metre. For comparison, A554 Table 5 allows 1.4 to 10.4 mm/m on square and rectangular tubing, depending on size.
- Straightness. A554 allows 0.76 mm in any 0.9 m on round tubing and 2.1 mm per metre on square and rectangular tubing. For shapes, state your own figure.
- Flatness, parallelism or symmetry on faces that locate or seal.
Only tighten the dimensions that matter. Every tight tolerance adds drawing passes, inspection time and cost.
5. Choose the grade
| Grade | Choose it for |
|---|---|
| 304 / 304L | General indoor and outdoor use away from salt and chlorides; the default for most shaped tube |
| 316 / 316L | Coastal and marine sites, swimming pools, de-icing salts, chemical environments |
| 430 | Indoor decorative and appliance parts where lower cost matters and corrosion exposure is mild |
| 201 | Indoor decorative use where cost is the main driver |
One point to check: if your project requires ASTM A554 certification, note that grade 201 is not listed in A554 Table 1, while 304, 304L, 316, 316L and 430 are. Choose a listed grade, or agree the specification with your supplier.
For the trade-offs between 304 and 316, see our 304 vs 316 vs 316L selection guide.
6. Specify the surface finish and the seam position
Common finishes for shaped tube:
- Mill finish (as welded, or annealed and pickled);
- Satin or hairline (180–320 grit);
- Mirror (400–600 grit);
- Electropolished.
For visible parts, two more details prevent disputes:
- Seam position. Welded shaped tube has a longitudinal seam. State which face it may be on, for example the hidden face of a handrail or the inside of a frame.
- Protective film on polished faces, and whether it must be laser-grade film for cutting.
ASTM A554 only requires the tube to be free of scale. Any special surface condition has to be stated in the order (Section 12.2).
7. Tooling and samples
A new profile usually needs new dies or rolls. This is the part of the quote buyers ask about most, so here is how we handle it:
- Check existing dies first. Send your drawing and we check our partner factories’ existing dies. Common profiles can often be matched, and if yours can, no new tooling is needed.
- New tooling is a one-time charge. For non-standard profiles, the tooling fee is charged once. It can normally be credited back against your orders once cumulative volume reaches an agreed tonnage, typically in the 5–20 ton range, or credited back in stages. The terms are agreed at quotation.
- Custom dies for your profile. Standard dies are shared. Dies made for a custom profile are kept for your orders under the terms agreed in the contract, including the repeat-order period.
- Samples in 7–15 days after the drawing is confirmed, depending on the profile’s complexity and the production schedule.
- Approve before production. We send cut cross-sections and a measurement report. Mass production starts only after your written approval.
8. Inspection and documents
For shaped tube, a caliper check is not enough. Ask for:
- Profile inspection of cut sections against your drawing, by optical profile comparison or coordinate measuring machine (CMM);
- Weld seam testing. Under ASTM A554, nondestructive testing is a supplementary requirement (S3), so the test (for example eddy current) and its acceptance limits must be written in the order;
- EN 10204 3.1 mill test certificate. Under A554, mill test reports are furnished when specified in the order (S4.1), so state it;
- Third-party inspection (for example SGS, BV or TÜV), arranged at order stage if your project requires it.
9. Cutting, marking and packaging
- Cut length and tolerance. A554 Table 4 gives cut-length tolerances by length and size if you have no requirement of your own.
- End finish: deburred, square cut, or mitred.
- Marking: heat number, grade and size on each bundle, for traceability to the certificate.
- Packaging: protective film, sleeves or wrapping so that faces do not rub, and seaworthy wooden cases for export.
10. RFQ checklist: copy and paste
- Drawing attached: DXF / DWG / STEP / PDF; critical dimensions marked
- Profile: oval / D / triangle / hex / slotted rail / custom
- Process preference: roll formed / cold drawn / supplier to advise
- Tolerances: critical dimensions __ ; wall ± _ ; corner radius ; twist mm/m ; straightness ___ mm/m
- Grade: 304 / 304L / 316 / 316L / 430 / 201 ; specification: ASTM A554 / EN 10296-2 / other
- Finish: mill / satin 180–320 / mirror 400–600 / electropolished ; seam position ______ ; protective film (Y/N)
- Samples required before production (Y/N)
- Tests and documents: eddy current / 3.1 certificate / third-party inspection / profile report
- Length __ ± _ ; quantity ; annual volume ___
- Packaging and marking: __ ; destination and Incoterm: ____
Frequently Asked Questions
Is there a standard tolerance for special-shaped stainless tube?
Not in the usual sense. ASTM A554 publishes tolerance tables for round, square and rectangular tubing only. For special shapes the dimensions are specified by the purchaser, and straightness on special requirements is agreed between purchaser and producer. Put the tolerances on your drawing.
Do I have to pay for tooling?
Only if no existing die fits your profile. New tooling is a one-time charge that can normally be credited back against your orders once cumulative volume reaches an agreed tonnage, typically 5–20 tons.
How long do samples take?
7–15 days after the drawing is confirmed, depending on the profile and the production schedule. Mass production starts after you approve the sample sections and measurement report in writing.
What is the minimum order for a custom profile?
Trial orders from 100–300 kg are supported for standard and custom profiles, subject to tooling.
Roll formed or cold drawn: which should I choose?
Roll forming suits architectural and structural profiles at medium to high volumes. Cold drawing gives tighter tolerances (about ±0.08–0.15 mm) and a more uniform wall, for precision fits and mechanisms.
How TeCarve supplies special-shaped tube
TeCarve is the exclusive export arm of two manufacturing partners in Foshan and Wenzhou, China. We supply special-shaped stainless steel tube in oval, D-shaped, triangular, hexagonal, slotted and fully custom profiles.
- Sections up to 200 mm, walls 0.5–5.0 mm; 201, 304, 304L, 316, 316L and 430
- Roll formed or cold drawn, to ASTM A554, EN 10296-2, JIS G3446 or GB/T 12770, or to your drawing
- Existing dies checked first; new tooling credited back against agreed volumes
- Samples in 7–15 days, with cross-sections and a measurement report for your approval
- EN 10204 3.1 mill test certificate with every shipment; third-party inspection arranged on request
- Trial orders from 100–300 kg; response within 24 hours at sales@tecarve.com
Related reading: Oval pipe & tube · Custom stainless steel tube fabrication · 304 vs 316 vs 316L selection guide · Decoration pipe & tube
