13920 Bf ^hot^ | Iso

| Shorter leg length (mm) | Permitted deviation (± minutes or mm/m) | |------------------------|------------------------------------------| | up to 400 | ±15' (0.25°) or 4 mm/m | | >400 to 1000 | ±10' (0.17°) or 3 mm/m | | >1000 to 2000 | ±7.5' (0.125°) or 2 mm/m | | >2000 to 4000 | ±5' (0.083°) or 1.5 mm/m | | >4000 | ±5' (0.083°) or 1 mm/m |

Note: Some drawings use "BF" as a shorthand for "Fine overall" – but strictly per ISO 13920, you must verify if they mean linear class F + angular class B. Occasionally, "BF" is used to mean "Class B – Fine" for both, but that is non-standard. Always confirm with the drawing's tolerance block. iso 13920 bf

| Symbol | Meaning | Applies to | |--------|---------|-------------| | | Fine class | Angular dimensions, straightness, flatness | | F | Fine class | Linear dimensions | | Shorter leg length (mm) | Permitted deviation

Introduction In welding fabrication, achieving perfect dimensions is often impractical and cost-prohibitive. ISO 13920 is the international standard that specifies general tolerances for linear and angular dimensions, as well as for straightness and flatness, of welded structures. | Symbol | Meaning | Applies to |