JIS G 3350 Light Gauge Steel Channels: Specification, Dimensions and Roll Forming Manufacturing Guide

1. Definition and Scope

JIS G 3350 (Light gauge steel sections for general structure) specifies product requirements for cold-formed light gauge steel sections used in building construction and other structural applications in Japan. The standard defines section shapes, standard sectional dimensions, sectional area, unit mass, chemical composition, mechanical properties, dimensional tolerances, and inspection requirements for the finished product.

JIS G 3350 covers several cold-formed profile types, including plain channels (light gauge channels), lipped channels, Z-sections, angle sections, and hat sections. Plain channels are commonly used as C-channel framing members. Sections may be formed from hot-rolled or cold-rolled steel sheet and strip. Galvanized and other coated products are covered separately in Annex A and are not part of the base SSC400 product grade requirements.

The standard designates product quality by the grade symbol SSC400. Feedstock material grades and coating designations are selected separately according to the referenced material standards and the purchaser’s requirements. Roll forming and press braking are typical manufacturing methods noted in the standard; specific roll forming parameters depend on manufacturer tooling design and production conditions.

For roll forming manufacturers, JIS G 3350 provides the product specification for profile geometry and quality verification. Tooling design, material selection, and inspection should reference the standard dimension tables and tolerance requirements. Additional fabrication features such as holes, slots, or miter cuts are normally specified on engineering drawings beyond the base cross-section defined in JIS G 3350.

2. Plain and Lipped Channel Dimensions

JIS G 3350 uses different designation formats by section type. Plain channels (Table 5) are designated H × A × B, where H is web height and A and B are flange widths (typically A = B for equal-leg plain channels). Lipped channels (Table 8) are designated H × A × C, where C is the lip length. All sections use a single plate thickness t. Corner radius is generally 1.5 t at the centerline of plate thickness unless otherwise agreed.

Standard sectional dimensions in JIS tables are representative values. Non-standard dimensions may be used by agreement between purchaser and manufacturer, with sectional area and unit mass calculated per Table 12 in JIS G 3350.

2.1 Selected Standard Sizes (JIS G 3350 Table 5 and Table 8)

The following sizes are excerpted from JIS G 3350 standard dimension tables. Plain channel values are from Table 5; lipped channel values are from Table 8.

2.2 Section Properties (JIS G 3350 Annex B, Tables B.1 and B.4)

Section properties for structural design are provided in JIS G 3350 Annex B. Values below correspond to the sizes listed in Section 2.1 and are taken from Annex B reference tables (including corner-radius effects).

Annex B values apply to nominal standard dimensions. Actual roll-formed properties may vary within JIS G 3350 Table 13 tolerance limits and should be confirmed for structural design.

3. Material Specification

JIS G 3350 specifies one product grade for light gauge sections. Feedstock is selected from applicable steel sheet and strip standards according to coating, strength, and forming requirements.

3.1 JIS G 3350 Product Grade

3.2 Typical Feedstock Standards (Reference)

The following material standards are commonly used as feedstock for JIS G 3350 channel roll forming. Mechanical values refer to the feedstock standard, not the finished section designation. Note: JIS G 3302 SGHC does not specify a guaranteed yield strength; the 205 MPa value shown is a typical reference for the underlying SPHC-type base metal and must not be used alone for structural design calculations. Use SGH400/SGH440 or order-specified SSC400 product testing where strength conformance is required.

3.3 Typical Feedstock Selection by Channel Size (Common Practice)

4. Dimensional Tolerances

JIS G 3350 Table 13 specifies shape and dimension tolerances for finished light gauge sections. Values below are from the standard. Coated feedstock thickness tolerances follow Annex A where applicable.

4.1 Cross-Section Tolerances (JIS G 3350 Table 13)

Cross-section dimensions and angle are measured at any point along the member length, excluding both end portions, per JIS G 3350 Section 9.

Note on twist: JIS G 3350 Table 13 does not tabulate a separate twist (ねじり) tolerance. The bow (曲がり) requirement above applies to vertical and lateral deviation of flat parts along the member length. Additional twist checks may be specified by purchaser agreement or internal QC.

4.1a Lip Length Tolerance for Lipped Channels (JIS G 3350 Table 13)

The following tolerance applies to lipped channel sections (Table 8) only. Plain channels in Section 2.1 do not have a lip dimension C.

4.2 Length Tolerance (JIS G 3350 Table 13)

Standard delivery lengths are 4.0 to 12.0 m per JIS G 3350 Table 11 (4000–12000 mm, by agreement). Cut-to-length tolerance on roll forming lines may be tighter by customer agreement but is not part of the base JIS length tolerance unless specified on the order.

5. Roll Forming Production

JIS G 3350 specifies product requirements for light gauge steel channels; it does not define roll forming line parameters. In commercial steel channel manufacturing, plain channels are commonly produced on roll forming lines configured for C-channel geometry, progressing from flat strip through incremental bend stages to the final profile.

5.1 Typical Roll Forming Considerations (Common Practice)

Typical roll forming lines for JIS G 3350 plain channels may include decoiler, leveler, pre-punch (if required), forming stands, side rolls, and flying or stop cutoff. Stand count, line speed, and equipment selection depend on profile size, material thickness, strength grade, and required tolerance level. Heavier sections and thicker feedstock generally require more forming passes and lower operating speeds than light gauge sizes.

Developed strip width is calculated by tooling engineers using the section geometry, neutral axis, bend allowance, and the nominal corner radius (generally 1.5 t per JIS G 3350). Symmetrical roll pass design helps minimize twist in the finished channel; asymmetric sequences may be used on some lines but require additional side rolls and overbend tuning.

5.2 Strip Width Calculation (Engineering Reference)

For plain channels, developed width is commonly estimated from web height, flange widths, thickness, and bend allowance. Actual coil width is confirmed during roll tooling design and trial production. Slit coil is typically ordered at or slightly above the calculated developed width to allow edge trim if needed.

6. Quality Inspection

JIS G 3350 requires dimensional verification against Table 13 tolerances and, when the order specifies SSC400 product grade, chemical analysis and tensile testing per Sections 11 and 12. When the order specifies JIS G 3350 cross-section geometry with a feedstock grade such as SGH400 (not SSC400 product designation), mechanical conformance is normally demonstrated by the feedstock mill test certificate; finished-product SSC400 tensile testing applies only when SSC400 is specified on the order.

7. Roll Forming Applications

JIS G 3350 light gauge steel channels serve as structural and non-structural framing elements in Japanese construction and industrial applications. C-channel roll forming is widely used in steel channel manufacturing for building frames, equipment supports, and accessory structures.

JIS G 3350 channels are supplied through Japanese steel service centers and building-material distributors, often with mill test certificates documenting SSC400 conformance, coating mass (where applicable), and dimensional inspection results.

7.1 Connection and Fabrication Details (Common Practice)