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ASME Standards for the Revision of Engineering Drawings

Tamara Wilhite is a technical writer, industrial engineer, mother of two, and published sci-fi and horror author.

ASME has issued standards for the proper documentation of drawing revisions

ASME has issued standards for the proper documentation of drawing revisions

Engineering Drawing

American Society of Mechanical Engineers standard ASME Y14.35M was issued in 1997 to describe the ASME-approved format for tracking revisions and other changes to engineering drawings. ASME Y14.35M was reaffirmed in 2003, and no changes were made at that time. It updated to the name ASME Y14.35 in 2014.

What does ASME Std Y14.35 mandate?

ASME Y14.35M Standard

ASME Y14.35M and the later ASME Y14.35 standard allow for changes to be made to drawings by adding and crossing out information on a drawing or by creating a new drawing revision.

The ASME drawing standards state that new drawings can be recorded as a new revision letter or as a new drawing number that supersedes the old one. The replaced drawing will be modified to note “replaced with change by drawing 1234567”. This ensures configuration management and product verification is handled correctly.

The first version of a drawing is identified by a revision dash “-“. After that, revision letters are used. Revision letters can be a single letter up to multiple letters.

All letters can be used as revision letters except I, O, Q, S, X, and Z. These letters are not allowed because they can be mistaken for numbers or for other letters. For example, a revision letter I can be mistaken for a 1 while an S can be mistaken for a 5. Revision letters must also be uppercase, to minimize confusion between a lowercase "l" and "1" and "I".

After the end of the revision letter sequence is used up, the next letter is added to the end. Revision letter Y is followed by revision AA. Revision AY is followed by BA. Revision DY is followed EA.

However, revision letters are not allowed to exceed three characters, so there is no revision greater than YYY. At this point, you should issue a new drawing number.

Revision columns are located in the upper right corner or next to drawing the title block. Revision columns include the revision letter of the drawing, a short description of the changes made between this revision and the prior one, and the date the revision was made or the revised drawing was approved. Revision columns frequently include the drafter who made the latest revisions.

ASME standards require parts to be labeled with the part number and revision letter per their manufacturing drawings

ASME standards require parts to be labeled with the part number and revision letter per their manufacturing drawings

ASME standard Y14.24 gives readers a list of when ASME engineering drawing standards like ASME Y14.35 apply. ASME Y14.1 defines the acceptable form of the revision history block.

ASME Y14.1 gives the ASME standard size and format used in engineering drawings.

ASME Y14.2 outlines the accepted line conventions and lettering used on engineering drawings. ASME Y14.3M describes the accepted forms of single, multiple, and sectional views used on engineering drawings.

ASME Y14.100 provides a list of standard engineering drawing practices recommended by the ASME. Depending on the customer or project, other ASME or ISO standards may also be required. And ASME drawing standards do not cover documentation control or configuration management at all.

Questions & Answers

Question: When an engineering drawing is revised to be completely different than the original by different engineers than the original drafter and checker, does that information in the title block change? Can the information in the title block ever be revised if it is unrepresentative of the revised work?

Answer: If car name X is radically revised in revision B, they could create revision A with rev B and still call it the same car and drawing number. If they turn a car into a plane, it should be a new drawing number.

Question: I want to know if a particular piece has 4 drawings associated to it and you make a change on one of the drawings, shouldn't all the drawings be changed to the same rev level? Meaning if they were Rev A then they all would change to Rev B?

Answer: No. Suppose the top level part is 1234567 rev A, and the child drawings are 23456 rev A and 78901 rev A. If 78901 rev A becomes rev B, the top level assembly needs to be updated to say if rev B is allowed on the parts list, but the related 23456 rev A stays rev A.

If changing one drawing changes everything that's associated with it, you would never stop churning out the updates.

Question: Should engineering drawings be numbered as Rev 1 or Rev 01?

Answer: 01, because you can end up with 28 revisions.

Question: Is the ASME standard rev1 or should it be REV1 when naming the file?

Answer: I've seen it written as both "Rev" and "REV".

Question: A child drawing was updated to a later revision - does the parent drawing need a revision update? The bill of material does identify the child item but no rev.

Answer: If the child item is still compatible with the parent part, no, you don't need to update it. If rev A doesn't fit but rev B does, specify that in the bill of materials.

Question: When a new revision is made, am I supposed to delete the old rev symbols? Say it’s rev C and I still have the rev a & b symbols on the drawing to show where the changes were made?

Answer: It is fine to leave several prior revisions along with the associated changes on the drawing so that people holding an older product know what it means.

Question: If I have a multi-page page document and rev sheet 1 and 4, do I update rev of all?

Answer: Short answer: yes, at least the title block.

Long answer: all document pages should refer to the same revision letter and version number so that people who are looking at a set of drawings know that they belong together.

Question: Do the revised standards of engineer drawings allow skipping item numbers in a bill of material?

Answer: Yes. You could have item 1, item 2, and item 4. You can avoid confusion for the reader by listing item 3 and having an obvious place holder dash in the BOM. Then it could be filled in as part of a later version of the BOM.

Question: What is the standard practice when the revision block is full (i.e. 5 lines) and the print is too small to add more rows?

Answer: I suggest referring directly to ASME Y14.100 for the solution.

Question: Is it ok to use NON instead of None in regards to engineering drawings? If not, why?

Answer: No. NON versus None is confusing. If you list a part or manufacturing supplies on the drawing and it isn't going to be used, put "N/A" for not applicable in the parts list. Or don't include that item on the parts list and drawing.

Question: What names go on an engineering drawing?

Answer: It is standard to list the name of the company so that anyone who sees the drawing knows who owns the intellectual property, the design. That typically goes in the title block. The names of the drafter and the person who approved the drawing also go in the drawing block.

Question: We use numbered Revs for prototype drawings, i.e. Rev 1, Rev 2 etc. When we are ready to release for production we change to letters i.e. Rev A, Release for Production, Rev B, Rev C etc. Sometimes at Rev A we still change things. Do changes at Rev A require a change letter symbol designation? Triangle/circle A to locate the change? Do the changes get recorded in the revision block?

Answer: In general, revisions numbers / versions 1 and 2 are for little changes and things in work, while revision letters are for major, released changes. When you make major changes, issue a formal revision letter change for the new drawing.

Question: Do we use revision triangles to denote changes for revisions during prototype changes? Like revision of Rev 3 to Rev 4?

Answer: Revision triangles are used to make it clear to someone you changed dimensions. Formally released drawings shouldn't have revision triangles. Just note in the revision description what you changed.

Question: If you have to update the drawing to a new revision, do you still leave the symbols of the old revision on the changes you made on the drawing and just add the new ones?

Answer: You have to have a record of the changes to the document SOMEWHERE. In newer product data management systems, you can simply change the revision from C to D and note the changes that go with revision D while the system tracks all the changes associated with earlier revisions. At least mention in the notes for revision D what changed so that those who see the new document know what has changed.

Question: How many revision rows do you leave on a drawing at one time? For example, if I am at Rev F, can I leave off Rev A, B, C and include D, E, F or just E, F?

Answer: I've seen drawings that showed the last 10 revision letters with a short explanation of what it meant. You should include at least the last several revision letters, as far back as there may be drawings in circulation to explain what has changed over time.

Question: Which short description should I use when dimensions are not modified, but just moved or relocated in a drawing?

Answer: Simply say "dimensions moved" or "dimensional references moved".

Question: If you have an assembly and need to revise a sub-component of the assembly for a typo on the drawing would that require the top assembly drawing do be revised as well? The change would not affect fit, form, or function of the top assembly.

Answer: If the revision letter of the subcomponent changes, the bill of material for the parent assembly needs to change IF it refers to child parts as having a specific revision. If it only calls for part 1234567-1 without a revision letter, then no change to the parent drawing is required.

Question: Does the ASME drawing standard allow skipping item numbers in a bill of​ material?

Answer: Allow, yes. However, you need to take care that you account for the skipped numbers so that people know it isn't an oversight.

Question: Is it a good practice to line through BOM items on an assembly drawing?

Answer: Yes, it is a holdover from drawing board days. The line through an item on the bill of materials with a note as to when it was eliminated actually helps when someone is reviewing an older version of the product or needs to retrofit it. It also helps them recognize errors in the parts list or assembly instructions if those were not changed when the drawing was.

Question: Suppose I have missed one dimension in the drawing but the basic design of the drawing is unchanged. Is it possible to change my engineering drawing without making a revision?

Answer: The revision letter should change, and review the drawing for other key dimensions you're missing.

Question: Does revision designation (-) only apply to engineering drawings?

Answer: Yes, though you can use revision "dash" for test plans and work instructions as well. ASME revision control rules, though, forbid using revision 0 (zero) because it could be mistaken for an O (the letter).

Question: What is the release date for the Asme Standards?

Answer: A release date is a date you officially release or publish the drawing. The release dates of drawing revisions show when the new drawing version is official. Anything built after that point typically has to be made to the new revision.

Question: If I have one item in the BOM, should I need to show the balloon in the drawing as per ASME?

Answer: Yes, I would recommend that. It would make things clear if manufacturing supplies or assembly hardware like screws are later called out.

Question: When should we use status IFC, IFA? Can we write IFC status on an already issued drawing for which construction has been already completed and some modifications done down the line?

Answer: AFC is approved for construction. That's the one you should build to. IFC is in review and not finalized. It shouldn't be used if not formally approved. Not sure what IFA is.

You should not be altering the approval status of documents when you have a drawing control process to maintain control of the documents; this ensures that no one builds to unapproved specs. And in construction, that's expensive.

Do not modify formally approved documents and switch the status. If you need to issue a new drawing revision to reflect changes, go through the drawing control status.

Question: Does solidworks allow you to use enter all the revision letters you are not using?

Answer: I know it allows you to reuse view letters, such as when you delete an angled view labeled view C. It should allow you to enter many revisions not visible on the current drawing such as notes you've eliminated part 38. It may not let you show all 20 revision letters on the document, but you may not have to, either.

Question: Does " Revision - "equal to REV NONE or do you need to put the - instead?

Answer: The dash would go in the revision block. An "A" would refer to the first revision of the original drawing. However, if you're dealing with a PDM system, it may not let you have "-", so you may have to start with the first released drawing as rev A.


Tamara Wilhite (author) from Fort Worth, Texas on January 24, 2020:

From what I have observed, the same revision letter system applies whether it is test plans or wiring diagrams.

Tim Marion on January 24, 2020:

Does this also apply to the labelling of electrical wiring in wiring diagrams where the use of lowercase and uppercase lettering is used?

Garry Reed from Dallas/Fort Worth, Texas on April 29, 2019:

Interesting. I was an on-the-board drafter for many years back in the olden days and all changes to defense system drawings where executed by ERs (Engineering Requests) and EOs (Engineering Orders) if my poor old brain remembers.

Even during modern times as a tech writer and logistics specialist doing all work via computer programs I had to stay abreast of drawing changes and pending changes, and as a logistics engineer even recommended some of those changes myself.

Tamara Wilhite (author) from Fort Worth, Texas on April 26, 2019:

I don't know how to handle documention within SAP.

denisewoods2019 on April 26, 2019:

I have a question: Can a description be changed in SAP system only adding dimensions to description without creating an ECO. No change is being made to the drawing or title block. Drawing title: Label, description in SAP- Label. When looking for a label drawing in the system( shouldn't they have dimensions in the description to make it easier to locate what your looking for? Question is: Can you add to the description without writing and ECO on an active part number.

Tamara Wilhite (author) from Fort Worth, Texas on July 10, 2018:

Update the most recent released drawing to the next revision letter.

James R Dunn on July 10, 2018:

I have a question about revisions. I recently found a drawing from my company that has the same revision letter used twice. What is the proper way to handle this mistake?

Tamara Wilhite (author) from Fort Worth, Texas on November 28, 2017:

MZ1 Form what I've seen, they use the same symbols for drawings. However, concentricity and symmetry differ. ISO uses geometric tolerancing and doesn't recognize that used by the ASME standards.

MZ1 on November 28, 2017:

Hello Tamara

Our company is certified lately to AS9100 standard

I’m looking for a linkage between:

ASME Y14.35M rules



I mean where should I find the ASME Y14.35M rules in AS9100 ?


Tamara Wilhite (author) from Fort Worth, Texas on March 08, 2017:

The "M" refers to metric version of standards like the older version of ASME Y14.34M; the "M" disappears when metric and non-metric standards are consolidated.

Steel Engineer from Kiev, Ukraine on January 31, 2014:

Worthwhile read. Thanks for sharing this.