En Iso 13920-bf <HD | 1080p>

If you are a design engineer, using this standard correctly will save your workshop hours of confusion.

Incorrect usage:

"USE STANDARD WELDING TOLERANCES"

Correct usage (per ISO guidelines):

"GENERAL TOLERANCES: EN ISO 13920 – B (MEDIUM). ALL OTHER DIMENSIONS ± 0.5 mm"

Advanced usage (with modifiers): If your "BF" actually means "B + Filter," you might add: en iso 13920-bf

"EN ISO 13920-B, BUT FLATNESS OF MOUNTING FACE F1 (reference surface) TO BE HELD TO CLASS A (±0.5 mm)"

This notation tells the welder: "Use Class B for most features, but tighten up this specific surface."

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.

However, the combination "BF" does not strictly exist in the standard's classification list (which lists AC, AD, BC, and BD). If you are a design engineer, using this

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.

(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).

If part A slides into part B with a clearance of 0.2 mm, do not use ISO 13920-B. Class B allows ±3 mm over 400 mm. Your sliding fit will jam or wobble. Use Class A or machine after welding. "USE STANDARD WELDING TOLERANCES"

| Term | Standard | Meaning | |------|----------|---------| | EN ISO 13920 | ISO 13920 | General tolerances for welded constructions | | Class C, D, E, F | ISO 13920 | Tolerance grades (C finest → F coarsest) | | BF | ISO 9692-1 | Butt weld preparation with Backing + Flat root face | | EN ISO 13920-BF | Invalid combo | Likely means: Tolerance Class F + Weld prep BF |