STKM13A or STPG370 — which tube do I order?

Same chemistry family, different job: STKM13A is mechanical/structural tube (JIS G3444) bought for machining and fabrication; STPG370 is pressure pipe (JIS G3454) bought for piping codes. Do not substitute one for the other on certified work.

Grades · Pipe & Tube Steel · STKM13A

STKM13A

Data verified

STKM13A is a JIS G3444 carbon steel tube for machine structural purposes — the 370 MPa class tube Japanese machinery makers use for frames, rollers and mechanical parts. Its chemistry window mirrors STPG370 but the standard, tolerances and flattening/flaring tests are written for mechanical tube, not pressure pipe.

DINE235 tube type (near)

AISI1020 tube type (near)

JISSTKM13A (JIS G3444)

CategoryPipe & Tube Steel

Chemical composition

Element	Content (%)
C	≤0.25
Si	≤0.35
Mn	0.30–0.90
P	≤0.040
S	≤0.040

Weight percent, per the governing standard ranges. Actual values per heat are on the mill certificate.

Properties

Tensile strength	≥370 MPa
Yield strength	≥215 MPa
Density	7.85 g/cm³
Product form	Carbon steel tube for machine structural use (JIS G3444)

Heat treatment

Supplied as-welded, drawn or annealed tube; no hardening (low carbon). Carburizing is possible for wear surfaces.

Equivalent grades

Standard	Designation
din	E235 tube type (near)
aisi	1020 tube type (near)
jis	STKM13A (JIS G3444)
gb	20 tube (near)

Compare side by side: STKM13A vs SAE 1020 · STKM13A vs STPG370

Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.

Applications & Processing

Applications: Machine frames, conveyor rollers, automotive and agricultural machinery tube, scaffolding-grade mechanical parts.

Processing: Welds and bends well; supplied in welded or seamless form with tube tolerances. Not a pressure-pipe grade — use STPG (JIS G3454) for pressure service.

FAQ

STKM13A or STPG370 — which tube do I order?: Same chemistry family, different job: STKM13A is mechanical/structural tube (JIS G3444) bought for machining and fabrication; STPG370 is pressure pipe (JIS G3454) bought for piping codes. Do not substitute one for the other on certified work.

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Source: JIS G3444 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.