En Iso 13920-bf Jun 2026

The feature is a combined designation for general tolerances in welded constructions. It specifies an accuracy level for both dimensional and geometric variations on technical drawings. The designation breaks down as follows:

: It provides a clear benchmark for what is considered an acceptable "standard" build in industrial fabrication.

is the specific "handshake" between the designer and the workshop: B (Linear/Angular Dimensions):

However, in practice, when designers write , they usually mean:

Refers to the tolerance class for linear dimensions. Typically, ISO 13920 classifies these as A (Fine), B (Medium), C (Coarse), or D (Very Coarse). Class B represents a "medium" tolerance level. en iso 13920-bf

In the world of metal fabrication, precision is relative. Achieving surgical accuracy on a massive steel girder is neither practical nor cost-effective. This is where comes into play. It provides a standardized framework for general tolerances in welded structures, ensuring that parts fit together without requiring the impossible level of precision typically reserved for machined components.

Linear values dictate lengths, widths, heights, and distances between parts: : ±1plus or minus 1 Over 30 to 120 mm : ±2plus or minus 2 Over 400 to 1,000 mm : ±3plus or minus 3 Over 1,000 to 2,000 mm : ±4plus or minus 4 Over 2,000 to 4,000 mm : ±6plus or minus 6 Angular Dimensions (Class B) ISO 13920 An Explained Guide to Welding General Tolerances

However, the combination does not strictly exist in the standard's classification list (which lists AC, AD, BC, and BD).

Angular deviations are measured across the of the angle being inspected. For Class B, these values are expressed proportionally to prevent catastrophic lever-arm misalignment over long spans: The feature is a combined designation for general

These values apply strictly to lengths, widths, heights, and thicknesses of welded fabrications. Per the ISO 13920 Guidelines , the allowed limits for Class B include: Nominal Size Range ( Class B Tolerance limit ( ±plus or minus ±plus or minus Over 30 up to 120 ±plus or minus Over 120 up to 400 ±plus or minus Over 400 up to 1,000 ±plus or minus Over 1,000 up to 2,000 ±plus or minus Over 2,000 up to 4,000 ±plus or minus Over 4,000 up to 8,000 ±plus or minus Over 8,000 up to 12,000 ±plus or minus 2. Angular Dimensions

For Class , the tolerances for common geometric features are defined. The value shown is the permitted deviation based on the length of the measured feature.

is a specific technical callout for general tolerances in welded constructions, where B represents the tolerance class for linear/angular dimensions and F represents the class for shape and position. 💡 🛠️ Decoding the "BF" Designation

is considered "medium" or customary workshop accuracy for welded parts. F (Shape and Position): This refers specifically to straightness, flatness, and parallelism is the specific "handshake" between the designer and

: Accuracy of angles between welded parts.

Choosing the right tolerance class is a matter of balancing cost with function. Too fine a tolerance (e.g., specifying Class A and E when only Class B and F are needed) will cause fabrication costs to rise sharply without providing additional functional benefit. Conversely, too coarse a tolerance may compromise the structure's safety or create assembly problems on site. The "BF" class is the industry standard for general engineering because it avoids the high costs associated with fine tolerances while ensuring the finished structure will assemble and function as intended.

When inspecting a part with "EN ISO 13920-BF":