En Iso 13920-bf
If you have a welded beam with a nominal length of 1000 mm:
This standard specifies tolerance classes (fine, medium, coarse) for:
It does not 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.
When a drawing specifies ISO 13920-BF, it is referring to:
Correction: In the ISO 13920 coding system, the second letter regarding geometrical tolerances is either C (Fine) or D (Medium). There is no "F" class for geometry. en iso 13920-bf
However, the combination "BF" does not strictly exist in the standard's classification list (which lists AC, AD, BC, and BD).
Why do people write "BF"? In many industrial contexts, particularly in heavy machinery and automotive supply chains, engineers often confuse or conflate standards. The most common standard classes are:
If you see ISO 13920-BF on a document, it is highly likely a typo or a non-standard internal code. It almost certainly implies Class B for linear dimensions. The "F" likely refers to a "Fine" requirement for geometry (which would make it ISO 13920-AD), or it is a typo for D (making it ISO 13920-BD).
Note: If the drawing explicitly writes "BF", you must clarify with the client. However, standard-compliant codes are: AC, AD, BC, BD. If you have a welded beam with a
(For the sake of this post, we will assume the user implies a Medium Linear / Medium Geometric requirement, which is standard Class BD, or is asking about the specifics of Class B).
EN ISO 13920 is the European adoption of the international standard ISO 13920:1996 – Welding – General tolerances for welded constructions.
It specifies general tolerances for linear and angular dimensions, flatness, straightness, and parallelism for welded structures, where no individual tolerances are indicated on the drawing.
The standard applies to:
To truly understand "EN ISO 13920-BF," you must know the numbers. Below are the key tolerance ranges for Class B (Medium). It does not define welding symbol positions (covered
In the world of metal fabrication and welding, precision is not an option—it is a requirement. However, achieving perfect theoretical dimensions in welded structures is virtually impossible due to thermal distortion, shrinkage, and material inconsistencies. This is where EN ISO 13920-BF comes into play.
If you have recently come across a technical drawing with the notation "EN ISO 13920-BF" in the title block, you may be wondering what it means for your production floor, your quality control department, or your budget. In this comprehensive guide, we will dissect the standard, explain the "BF" designation, and show you how to apply it correctly to avoid costly rework.
| Class | Typical use | |-------|--------------| | C | Fine – machined parts, precise jigs | | D | Medium – general structural steelwork | | E | Coarse – large fabrications, shipbuilding | | F | Very coarse – flame-cut plates, heavy beams |
Default for unmarked drawings is usually Class D.