A drawing is a binding contractual document. The drawing and all terms and symbols used must be unambiguous!

In order to reduce the risk of incorrect interpretation of the requirements in the drawing, it is recommend to stick as much as possible, to standards definitions, thus ensuring that in any place and even in 20 years or more the drawing would still be clear and unambiguous.

In many places it is common knowledge that the meaning of the term TYPICAL in the drawing – is something that is repeated multiple times (for example: Radius 12 in Figure 1), meaning that all radii in the drawing are 12.

Figure 1

The source of this definition is MIL-STD-8C from 1963.

3.11 Typical

The term “typical,” when associated with a dimension or feature, means that this dimension or feature applies to the locations that appear to be identical in the size and configuration. The tolerance stated for a dimension labeled “typical” also applies to each identical feature.

This standard was retired on January 1st, 1968 (MIL-STD-8C Notice 1), and was superseded by American Standard Y14.5-1966 in which the Term “TYPICAL” is not defined (nor in subsequent revisions of the Y14.5 standard) and therefore has no meaning. In other words, anyone receiving the drawing, who does not share the tribal knowledge, may, at best, contact someone to find out what this notation means, or may do as they see fit…

In order to indicate a repeated requirement, the number of repetitions needs to be specified (similar to the number of holes specified in Figure 1 or the number of repetitions X the dimension in question, as shown in Figure 2 for the radii and the holes).

Figure 2 – ASME

Only recently, in ASME Y14.41 2012 edition, a definition of the term “TYPICAL” appeared in a GD&T Standard, but this definition is completely different from the one defined in MIL-STD-8C. The word “TYPICAL” in the 2012 edition is used to indicate a non-compulsory suggestion or recommendation, for guidance only.

ASME Y14.41-2012 1.3.1

(d) The words “TYPICAL,” “example,” “for reference,” or the Latin abbreviation “e.g.” indicate suggestions given for guidance only.

As shown in the example in Figure 2.

The use of TYPICAL in Figure 2 serves as a recommendation to use a 7.8 diameter drill, for a pre-reamed hole, before reaming the six holes, and this is a non-compulsory recommendation. In any case, the requirement is that the final hole will be 8H8.

In ISO standards, the term TYPICAL does not exist!!! as well.

In order to indicate a repeated requirement, the number of repetitions needs to be specified, and the symbol for multiplication is “x” (lowercase letter), as illustrated in Figure 3.

Figure 3 – ISO

In summary:

In order to indicate that a dimension or a feature is repeated,

the number of repetitions needs to be specified!

The use of the word TYPICAL for this purpose is misleading (except when used on drawings that reference MIL-STD-8C, which was made obsolete by the US Department of Defense in 1968).

In light of the new definition of TYPICAL in the ASME Y14.41-2012 standard, which is used to indicate a non-compulsory recommendation, there is an added risk of misinterpretation.

Bottom line is,

even if we did something “a thousand times” and “everyone” understands what it means,

it may be common and accepted,

but it does not make it conforming to a Standard!