En Iso 13920-bf __exclusive__ Page

simplifies technical drawings by removing the need for hundreds of individual plus or minus

: Represents the tolerance class for linear and angular dimensions . Class B is considered "medium" or "customary workshop accuracy".

This post breaks down the EN ISO 13920 standard, specifically focusing on the tolerance class, to help you understand when to use it and how to apply it.

EN ISO 13920 is a European standard titled, "Welding — General tolerances for welded constructions — Dimensions for lengths and angles — Shape and position" . It is the European adoption of the international standard ISO 13920:2023, having been approved by CEN (European Committee for Standardization) without any modification. This standard is a critical tool in the manufacturing and engineering industries, as it specifies general tolerances for all welded structures, including weldments, welding assemblies, and other fabricated constructions.

The standard applies to:

| Nominal Size Range (mm) | Permitted Deviation (Class B) | | :--- | :--- | | 30 to 120 | ± 2 mm | | 120 to 400 | ± 3 mm | | 400 to 1,000 | ± 4 mm | | 1,000 to 2,000 | ± 5 mm | | 2,000 to 4,000 | ± 6 mm | | 4,000 to 8,000 | ± 7 mm | | > 8,000 | ± 8 mm + 0.5 mm per 1,000 mm |

: Represents the tolerance class for straightness, flatness, and parallelism . Core Tolerance Areas This standard provides specific allowable deviations for:

EN ISO 13920 is rarely used in isolation. It is part of a complete quality system and is often specified alongside other international standards to provide comprehensive manufacturing instructions. A typical drawing might contain a list in its title block referencing:

This class governs tolerances for straightness, flatness, and parallelism. Key Tolerance Categories ISO 13920 standard en iso 13920-bf

: The letter "F" represents the tolerance class for geometric characteristics such as straightness, flatness, parallelism, and perpendicularity. The standard defines four such classes for geometric tolerances, denoted E , F , G , and H , with "E" being the finest and "H" the coarsest.

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Stop guessing and start specifying. Are you using BF for your general steelwork, or do you prefer a tighter tolerance?

If your assembly requires high-precision robotic integration later, BF might be too loose. But for 90% of general structural steel, it’s the gold standard for balancing cost and quality. simplifies technical drawings by removing the need for

If a junction has a 90° angle, the F (Medium) class might allow a deviation of ± 1° or ± 2°, depending on the leg length.

If the final measurement shows length = 2,008 mm (violation by 3 mm), the part fails. The solution? Re-cut side members 5 mm short next time to compensate for weld shrinkage.

You will most often see this code on technical drawings for: : Large structural steel assemblies. High Voltage Equipment : Such as corona rings and shields.

: By using general tolerances, manufacturers can avoid the high costs of unnecessary high-precision machining where it isn't functional. Typical Applications EN ISO 13920 is a European standard titled,

For the "F" class in shape and position tolerances (covering straightness, flatness, and parallelism), the permissible deviation (in millimeters) depends on the nominal dimension of the inspected feature:

The main criterion for selecting a particular tolerance class is based on the functional requirements that must be met for the structure to perform as intended.