Heat Treated Tight Tolerance 4130 Chromoly Steel Tube for Chassis Fabrication

Product Description

Product Description

State the STKM Grade and Manufacturing Route

JIS G 3445 specifies carbon steel tubes used for machine structures, including machinery, automobiles, bicycles, furniture and appliances.

Because the standard is broader than one manufacturing route, this page is deliberately limited to seamless tube. The order should identify the JIS edition, STKM grade, seamless method, dimensions, heat treatment, surface, tests and component application.

Product focus: round seamless carbon steel tube for machine structures. The product must not be described only as JIS G 3445 without also stating the required manufacturing route.

DIMENSIONS AND TOLERANCES

Control Fit for Japanese Machine-Part Drawings

Define the dimension that drives assembly, machining stock or finished component performance.

≡ OD  Outside Diameter  :        State the nominal size and ordered tolerance basis.
≡ ID    Inside Diameter     :       Control directly where component fit or machining stock requires it.

≡ WT  Wall Thickness      :       Confirm nominal wall and allowable variation before production.

≡ O     Roundness             :        Review for chucking, forming, sealing and component assembly.

≡ S     Straightness           :       Define the inspection method and application requirement on the order.

≡ Ra  Surface Quality       :       State visual, roughness or downstream-finishing requirements where needed.

Specification

IMPORTANT PARAMETERS
Factory capability and purchasing controls for seamless JIS G 3445 enquiries.
Product type	Round seamless carbon steel tube for machine structure
Standard focus	JIS G 3445:2025, edition confirmed on the order
Manufacturing route	Seamless route must be stated separately
Common grade directions	STKM11A / STKM12A / STKM13A or C, subject to review
Outside diameter	15-70 mm
Wall thickness	1-14 mm
Length	Random, fixed or cut-to-length according to order
Heat-treatment condition	Defined by grade, manufacturing route and purchase requirement
Surface	Bare, oiled or order-specific finish where available
Documentation	Material and inspection documentation as specified
Not every OD and wall combination is available in every grade, condition or tolerance class. Final feasibility is confirmed against the complete purchase specification.

steel grade	chemical composition%
	C	Si	Mn	P	S
STKM11A	≤0.12	≤0.35	≤0.60	≤0.040	≤0.040
STKM12A	≤0.20	≤0.35	≤0.60	≤0.040	≤0.040
STKM12B
STKM12C
STKM13A	≤0.25	≤0.35	0.30-0.90	≤0.040	≤0.040
STKM13B
STKM13C
STKM14A	≤0.30	≤0.35	0.30-1.00	≤0.040	≤0.040
STKM14B
STKM14C
mechanical property
steel grade	Tensile strength(Mpa)		Yield strength(Mpa)		Elongation(%)
STKM11A	≥295				≥35
STKM12A	≥345		≥175		≥35
STKM12B	≥390		≥275		≥25
STKM12C	≥470		≥355		≥20
STKM13A	≥375		≥215		≥30
STKM13B	≥440		≥305		≥20
STKM13C	≥510		≥380		≥15
STKM14A	≥410		≥245		≥25
STKM14B	≥500		≥355		≥15
STKM14C	≥550		≥410		≥15

Applications

Carbon Steel Tube for Machine Structures

≡ 01     Automotive Parts                                          Sleeves, supports and tube-based components

≡ 02     Motorcycle Parts                                          Steering, suspension and structural tube blanks

≡ 03     Bicycle Components                                    Tube-based frame and mechanical parts

≡ 04     Machine Components                                  Spacers, collars, supports and hollow parts

≡ 05     Furniture Mechanisms                                 Precision tubular mechanical members

≡ 06     Appliance Parts                                            Dimension-controlled tube components

≡ 07     Bushings and Sleeves                                 Cut rings and machined blanks

≡ 08     Custom Assemblies                                    Drawing-based seamless tubular parts

Prepare STKM Tube for Component Assembly

Cutting and machining can be matched to the Japanese drawing when datum and inspection requirements are clear.

Precision Cutting and Chamfering:

Fixed and cut-to-length supply

CNC Machining  :

Turning , Milling and Drilling

Honing and Skived & Roller Burnished   :

Precision internal surface

Custom Machining:

Components according to drawings

INSPECTION AND TRACEABILITY

Link the STKM Grade to the Seamless Tube Lot

≡ Material identity                                  ≡  Chemical composition

≡ Tensile properties                               ≡  Hardness where required

≡ OD / ID / wall                                       ≡   Roundness

≡ Straightness                                        ≡  Surface inspection

≡ Roughness if ordered                        ≡  NDT if ordered

Inspection follows the ordered JIS edition, grade, route and purchase specification. Additional surface, dimensional or NDT requirements must be stated before production.

Global Precision Steel Tube Standards and  Product Network

Each page answers a different market and purchasing intent while sharing one precision-tube manufacturing framework.

Different standards define different scopes, grades, manufacturing routes and acceptance rules. Similar grade names or historical references must not be treated as automatic equivalents.The finished store structure can connect standard pages to processing and application products.

JIS G 3445 Seamless Machine Structure Tube Purchasing Questions

Q:  What does JIS G 3445 cover?

A:  It covers carbon steel tubes for machine structures such as machinery, automobiles, bicycles, furniture and appliances.

Q: Is every JIS G 3445 tube seamless?

A:  Do not assume so. This product page is limited to seamless tube, and the manufacturing route should be explicitly stated on the order.

Q: Which STKM grade should be used?

A:  Use the full grade and suffix from the drawing or engineering requirement. Grade substitution requires technical approval.

Q: What is the confirmed factory size range?

A:  The confirmed range is 15-70 mm OD and 1-14 mm wall, subject to grade, condition and tolerance review.

Q: Can tubes be supplied as cut or machined parts?

A:  Yes. Cutting, chamfering, drilling, threading and CNC turning can be reviewed from the drawing.

Q: What information is required for quotation?

A:  Provide the JIS edition, full STKM grade, seamless route, dimensions, condition, tolerances, tests, quantity and component use.