The suffix brings together two independent metrics from the standard:
EN ISO 13920 - B F │ │ │ └── Class F: Form & Position Tolerances │ (Straightness, Flatness, Parallelism) │ └──── Class B: Dimensional Tolerances (Linear & Angular Dimensions) 1. The "B" Suffice: Linear and Angular Dimensions
However, in practice, when designers write , they usually mean: en iso 13920-bf
Clarification: The official ISO 13920 does list a class "BF." Instead, the correct notation on a drawing should be something like: "General tolerances: ISO 13920-B" or "ISO 13920 – Class B." However, in industry practice, "EN ISO 13920-BF" is widely used to denote Class B tolerances for general fabrication (F = Fabrication). For the purpose of this article, we will treat "BF" as Class B applied to welded fabrications (length, angle, flatness, and symmetry).
Q: Can EN ISO 13920-BF be used for non-welded constructions? A: No, the standard is specifically designed for welded constructions and parts. Other standards may apply to non-welded constructions. The suffix brings together two independent metrics from
(full title: Welding — General tolerances for welded constructions — Linear and angular dimensions — Shape and position ) is the European adoption of the international ISO standard. It serves as a universal reference for permissible deviations in welded assemblies.
This specifies the allowable variations for geometric attributes such as straightness, flatness, and parallelism. Key Tolerance Areas Q: Can EN ISO 13920-BF be used for non-welded constructions
The selection of a tolerance class has a direct impact on manufacturing cost, complexity, and risk. The "BF" combination is widely used because it represents a practical balance between precision and economic reality.
: The letter "B" represents the tolerance class for general linear and angular dimensions. EN ISO 13920 categorizes acceptable deviations into four tolerance classes based on customary workshop accuracy:
It define welding symbol positions (covered by ISO 2553), but ISO 13920-BF is an internal drawing notation referencing backing weld requirements in conjunction with tolerances.