Hot Rolled Angle Steel Thickness Tolerance and Negative Deviation

Why the Angle You Receive Is Lighter Than the Angle You Ordered

A fabricator orders 40 tons of L 75 x 75 x 6 angle against theoretical weight, receives the material, weighs it, and finds 36.5 tons on the ticket. Nobody cheated. The difference is negative deviation: the mill is allowed to roll the leg thickness slightly below nominal, and within the tolerance the piece still passes. The trouble is that the deviation is applied to the thickness, and thickness is what the weight formula is built from, so a small negative deviation becomes a large weight shortfall.

This matters because most angle steel in Asia is bought and sold on theoretical weight, not actual weight. If the contract says theoretical weight and the tolerance allows the mill to run thin, you pay for steel you do not receive. The fix is not to argue about it on arrival; it is to write the tolerance and the weighing basis into the purchase order.

The Tolerance Rules That Decide It

Three standards cover this and they are not identical.

Standard	Region	Thickness tolerance on angles	Weight tolerance
GB/T 706	China	Typically minus 0.3 to minus 0.6 mm on t	Plus or minus 5% per lot
EN 10056-2	Europe	Class-based, roughly minus 0.4 to minus 1.0 mm	Plus or minus 6% per lot
ASTM A6	USA	Depends on thickness range and leg width	Plus or minus 2.5% per lot

Note the weight tolerance: GB/T 706 allows up to 5% under, EN 10056-2 up to 6% under, while ASTM A6 is tighter at 2.5%. This is often the real commercial difference between an EN order and a GB order, not the unit price.

Theoretical Weight vs Actual Weight: Where the Money Goes

The example below uses L 75 x 75 x 6. The published theoretical mass is 6.905 kg/m, which includes the root radius.

Item	Value
Nominal thickness	6.0 mm
Theoretical mass	6.905 kg/m
Actual thickness if 5.6 mm	about 6.35 kg/m
Shortfall	about 0.55 kg/m, roughly 8%
On 40 t ordered	about 3.2 t not received

Run a sanity check before you sign the order: multiply the standard mass per metre by the ordered length and confirm the supplier’s tonnage agrees with your own figure. If the supplier has quoted from a thinner actual thickness instead of the standard mass, the shortfall will show up on the scale at destination. An 8% shortfall on a 40 ton order is more than three tons of steel, and on a theoretical-weight contract the buyer pays for material that is not in the truck. The mill is not in breach as long as it stays inside the standard; the buyer is simply exposed to the standard, and the buyer can close that exposure in the specification.

The Other Tolerances You Should Know

Thickness is the expensive one, but the section has several other dimensions.

• Leg length. Typically plus or minus 1.0 to 1.5 mm depending on standard and class.
• Out of square. The included angle should be within about 1 degree of 90 degrees.
• Camber and straightness. Usually 0.2% of length, so about 12 mm over 6 m.
• Length. Fixed lengths to plus 20 mm, or random lengths within a stated range.
• Twist. Limited as a percentage of the leg length.

Ask for these on the mill test certificate or the pre-shipment inspection report, not as an afterthought.

How to Write the PO So You Get What You Pay For

The following clauses remove almost all of the argument.

• State the standard and class. Write GB/T 706 or EN 10056-2 Class 1 or 2, not just the size.
• Cap the negative thickness deviation. For example, minimum leg thickness 5.8 mm on nominal 6 mm.
• State the weighing basis. Theoretical weight or actual weight, and if theoretical, quote the standard mass you are using.
• Tighten the lot weight tolerance. Ask for plus or minus 3% per lot, written in the contract.
• Require third-party weighing. SGS or BV weighing at load port, with the report on the shipping documents.
• Reserve the right to reject. Say that a lot outside the agreed weight tolerance can be rejected or settled by price adjustment.

Buyers who buy on actual weight avoid the issue entirely, but actual weight often carries a small price premium because the seller carries the leveling risk. For most structural fabricators a theoretical-weight contract with a capped negative deviation is the best compromise.

Send us the angle sizes, the standard and class, your required tolerance on thickness and the tonnage per size, and we will confirm what the mill can hold and quote it with a third-party weighing report included.