Choosing the correct size and thickness for mild steel (MS) flats keeps your structure safe, reduces waste, and saves money. This quick, practical guide walks you through the steps—function, loads, fabrication, weight calculations, and procurement—so you pick the right flat bar every time.
1. Start with function and load
Ask what the MS flats will do in your project.
- Load-bearing (bracing, light frames): prioritize thickness and cross-sectional area for strength.
- Decorative or non-structural (grills, trims, furniture): appearance and ease of fabrication matter more than high thickness.
- Machine or wear surfaces: choose sizes that allow for machining or surface treatments.
For structural uses, consult an engineer or structural table for required section modulus or allowable stress. For shop/fabrication work, practical rules below will help.
2. Typical size ranges and practical rules of thumb
Common widths: 25 mm to 150 mm.
Common thicknesses: 3 mm to 25 mm.
Rules of thumb:
- For light bracing or ties — 25–40 mm width, 4–6 mm thickness.
- For moderate loads and structural cross ties — 50–75 mm width, 6–12 mm thickness.
- For heavier members, bases or bearing strips — 100 mm+ width and 12–20 mm thickness.
These are starting points; always verify with load calculations for critical structural elements.
3. Weight calculation (quick way to estimate material)
Weight helps you estimate cost, transport and handling. Use this straightforward formula:
Weight (kg) = Width (mm) × Thickness (mm) × Length (m) × 0.00785
Explanation: 0.00785 = steel density (7850 kg/m³) adjusted for mm→m conversion.
Example: a flat 50 mm wide, 6 mm thick, and 2 m long:
- Multiply sizes: 50 × 6 = 300.
- Multiply by length: 300 × 2 = 600.
- Multiply by factor: 600 × 0.00785 = 4.71 kg.
So one 2 m piece weighs 4.71 kg. Use this to calculate total weight for orders and truck loading.
4. Fabrication and handling considerations
- Welding: Thinner flats (≤4 mm) can distort easily; tack-weld and use sequence welding. For thicker flats, ensure preheat where required.
- Bending/Forming: Flats bend better along the width than across thickness. Minimum bend radius depends on thickness and steel grade; test a sample when detail-critical.
- Drilling/Cutting: Thicker flats require more robust cutting and drilling tools—plan tooling and cycle time.
- Surface finish: If flats will be visible, allow for grinding/polishing allowances or specify mill finish vs cleaned/fettled.
5. Corrosion protection and environment
If the flat will be outdoors or exposed to moisture:
- Consider galvanizing for long life (preferred for exposed structural members).
- Powder coating or paint is fine for decorative use but needs maintenance.
- For marine or highly corrosive environments, consider alternative materials (stainless) or sacrificial design.
6. Procurement tips — what to specify to the supplier
To avoid surprises, include these in your PO or drawing:
- Exact width × thickness × length (e.g., 50 × 6 × 2000 mm).
- Steel grade or standard (if required): e.g., mild steel conforming to a national standard or plain carbon steel.
- Tolerance and straightness requirements.
- Surface finish (mill, pickled, galvanized, painted).
- Quantity by weight and by number of pieces; include packing/transport instructions.
- Delivery and cutting requirements (if you want pre-cut lengths).
7. Quick selection checklist
- Define function (load vs decorative).
- Choose width for bearing area and thickness for bending strength.
- Calculate weight to estimate cost and logistics.
- Check fabrication methods and adjust thickness for welding/bending.
- Specify corrosion protection based on environment.
- Put clear dimensions, tolerances and finish in purchase documents.
Conclusion
Picking the right MS flat is a balance between structural need, fabrication ease, cost, and durability. Start with function and loads, use the weight formula to plan logistics, and be explicit in procurement to avoid rework. If you tell me the intended use and approximate loads or dimensions, I can suggest specific sizes or produce a short procurement spec sheet you can use with suppliers.
