We supply carbon steel tube to JIS G3445 for machine structural use. This is the standard Japanese and Southeast Asian buyers write for motorcycle frames, fork parts, shock absorber bodies and general machinery components.
Price: quoted per specification. Steel prices move with the raw material market, so every quotation is confirmed at the time of order.
Specifications
- Standard: JIS G3445 carbon steel tube for machine structural purposes
- Steel grade: STKM11A, STKM12A, STKM12B, STKM12C, STKM13A, STKM13B, STKM13C
- Size range: Outside diameter and wall quoted to drawing
- Delivery condition: Hot finished or cold drawn as agreed
STKM grades and where they are used
JIS G3445 lists the STKM series; the number is the strength family and the letter is the forming or drawing condition the mill guarantees. The names matter because a Southeast Asian drawing usually quotes the JIS grade rather than an EN or AISI one.
| Grade | Character | Where it is normally used |
|---|---|---|
| STKM 11A / 11B / 11C | Lowest carbon of the series, most formable | Bent parts, frames, brackets, general forming |
| STKM 12A / 12B / 12C | Medium carbon, machinable | Fork parts, shock bodies, machined sleeves |
| STKM 13A / 13B / 13C | Higher strength of the common trio | Loaded structural tube, suspension parts |
| STKM 17, 20 | Higher strength still, less formable | Parts that see load rather than forming |
The A, B and C suffix is a condition, not a strength step you can assume: check the mechanical table of the edition your customer cites before you substitute one for another.
Seamless or welded
JIS G3445 covers both, which is where most purchase order arguments start. The same grade name can be supplied as seamless or as welded and drawn, and the two behave differently under pressure and under bending. If the drawing only says “JIS G3445 STKM 12A”, confirm the manufacturing route before the order, not after the tubes arrive.
What to specify in the order
| Item | What to write | Why it matters |
|---|---|---|
| Size | Outside diameter × wall, tolerance class | Sets price and what can be held |
| Grade | STKM 12A, with the edition year if your customer cites one | Grade tables differ between editions |
| Route | Seamless, or welded and drawn | The standard allows both and they behave differently |
| Condition | As drawn or annealed | Decides whether the part can be bent after delivery |
| Tests | Tensile, flattening, dimensions; hydrostatic if needed | Without them there is nothing to submit at inspection |
Packing and export
Tubes are bundled to a weight the receiving crew can lift, oiled, end-capped and wrapped, with wooden cases where the route calls for it. Documents are issued in English. For buyers in Vietnam, Thailand and Indonesia who need the certificate to match a JIS drawing, the certificate states the grade and the standard edition so the incoming inspection does not have to argue about which table applies.
Typical applications
- Motorcycle frames and fork parts
- Shock absorber bodies
- Automotive components
- Machinery structural parts
Standard reference: see our JIS G3445 standard page for grades, delivery conditions and tolerances.
Quality and packing: tubes are protected with anti-rust oil and packed seaworthy, in wooden cases where agreed. Each lot is tested for chemical composition, yield and tensile strength, flattening, elongation and dimensions, with visual inspection and NDT available on request.
Request a quotation: send your size list or drawing through our contact page. We reply within one working day with price, tolerance and lead time.