: Defines limits for straightness and flatness based on the largest dimension of the part. Application Rules ISO 13920 An Explained Guide to Welding General Tolerances
The suffix brings together two independent metrics from the standard:
The code "BF" consists of two distinct tolerance classes defined in ISO 13920 :
The overarching international standard defining general tolerances for welded assemblies. It ensures basic manufacturing accountability independent of individual dimension labeling.
Here is the breakdown:
Providing a clear basis for inspection and acceptance.
The standard is applicable to a vast array of welded structures across numerous industries, including rail vehicles, motor vehicles, crane construction, steel construction, machinery, and shipbuilding. In practice, a drawing specifying "BF" might be used for:
: Represents the tolerance class for shape and position (such as straightness, flatness, and parallelism). Tolerance Tables for EN ISO 13920-BF
This specification is commonly found on drawings for industrial equipment where standard welding precision is required without the need for high-precision machining. Examples include: en iso 13920-bf
: If a critical feature requires tighter control than what Class BF provides, that specific dimension must be toleranced individually on the drawing. The individual tolerance always overrides the general standard.
Before diving into the "BF" subclass, it is essential to understand the parent standard.
(ISO 13920 has no BF). It most likely means: "Weld edge preparation type BF according to ISO 9692-1, with general tolerances according to EN ISO 13920."
+--------------------------------------------+ | DESIGNED BY: J. Doe | DATE: 2026-05-31 | +--------------------------------------------+ | GENERAL TOLERANCES FOR WELDED STRUCTURES: | | EN ISO 13920-BF | +--------------------------------------------+ Use code with caution. : Defines limits for straightness and flatness based
Source: DIN EN ISO 13920 Standard.
These deviations are determined by measuring the longest external dimension of the welded structure or surface. Nominal Size Range of Longest Side (mm) Tolerance Class F (mm) Over 400 to 1000 Over 1000 to 2000 Over 2000 to 4000 Over 4000 to 8000 Over 8000 to 12000 Over 12000 to 16000 Over 16000 to 20000 Over 20000 Why Use EN ISO 13920-BF?
Specifying on a contract or purchase order is not just a suggestion—it is a contractual obligation.
: Represented by uppercase letters (E, F, G, H). Here is the breakdown: Providing a clear basis