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Short answer: In SOLIDWORKS, a balloon shows the item number from the BOM table it is linked to. A mismatch usually means one of three things: the balloon is linked to a different BOM, or to none; the BOM's item numbering was changed after the balloons were placed; or the view shows a different configuration or BOM structure (top-level, parts-only or indented) from the one the BOM uses. Fix the link and the numbering first, then re-check every balloon.
Steps
1. Check which BOM the view is linked to. Drawing views can be linked to a specific BOM table, so if there is more than one BOM on the sheet, balloons can follow the wrong one.
2. Check the configuration. The view's referenced configuration and the BOM's configuration must match.
3. Check the BOM type. A parts-only BOM numbers parts differently from an indented one. In an indented BOM, balloons can show detailed numbers such as 2.1.
4. Check the item number settings. Look at the start number, the increment, and whether the order follows assembly order. If you re-sort the table, the numbers can change unless they are locked.
5. Look for manual overrides. A balloon with typed text is no longer linked. Replace it with a linked balloon.
6. Re-run AutoBalloon after you fix the structure, if that is your practice, then tidy the placement.
Worked example (generic)
An assembly drawing shows balloon 7 pointing at a screw, but item 7 in the BOM is a bracket. Investigation shows that the BOM was re-sorted by part number after the balloons were placed, which renumbered the items. The designer turns off re-sort renumbering, restores assembly order and confirms that every balloon matches its item.
Common mistakes
- Typing item numbers into balloons by hand.
- Two BOMs on one sheet with no clear view link.
- Changing the BOM type late in the drawing.
- Not re-checking balloons after a component replacement.
More causes and how to check each one
1. Component pattern or mirror instances. All instances of a part share one BOM row. A balloon on any instance shows that row's number. If one instance is a different configuration, it gets its own row, and a balloon on it shows a different number. That is correct, but it surprises people.
2. Envelopes and excluded components. A balloon on an excluded component can't show an item number, because there is no row. Either include the component or remove the balloon.
3. Subassembly display settings. If a subassembly's BOM option is set to dissolve or promote its children, a balloon on the subassembly no longer matches a row. Balloon the children instead.
4. Multiple sheets. A balloon on sheet 2 can be linked to the BOM on sheet 1. Check the view's BOM link on every sheet.
5. Stacked balloons. Each balloon in a stack is linked separately. Check all of them, not only the top one.
6. Copied views. A view copied from another drawing may keep a link to a BOM that no longer exists there.
A checking routine before release
- Turn on a display that highlights unlinked or overridden balloons, where your version supports it. Otherwise, click a sample of balloons and confirm that the BOM row highlights.
- Count BOM rows and count distinct balloon numbers. Every BOM row should have at least one balloon, unless your standard allows unballooned rows.
- Check one item in each category: a made part, a purchased part, a fastener, a subassembly.
- After any component replacement, re-run the check. Replacement is the most common time balloons silently change.
A second worked example (generic)
A gas cabinet drawing has two BOMs: an indented BOM on sheet 1 and a parts-only BOM on sheet 3 for purchasing. Balloons on sheet 2 show numbers like 4.2, but the purchasing team reads them against the parts-only list, where item 4.2 doesn't exist. The views on sheet 2 are linked to the indented BOM, which is correct for assembly, but nobody stated it. The designer adds a note to sheet 2, "Balloons refer to BOM on sheet 1," and keeps the parts-only BOM without balloons. The numbers didn't change. The fix was making the link explicit.
FAQ
Can I lock item numbers?
Recent SOLIDWORKS versions let you keep or lock the numbering. See the BOM properties for your version.
Why does a balloon show "?"
It has usually lost its link to a component or BOM row. Re-attach it.
Should purchased hardware be ballooned?
Yes, if it is in the BOM. Every BOM item should be identifiable on the drawing.
Why do two instances of the same part show different numbers?
They are probably different configurations, which makes them different BOM rows.
Can one view link to two BOMs?
A view's balloons follow one BOM at a time. Use separate views if you need both.
Should I re-balloon after every change?
No, but re-check the links after replacements, configuration changes and BOM type changes.
Do balloons update automatically when the BOM is re-sorted?
Linked balloons follow the item number of their row, so re-sorting can change them. Lock item numbers before release if your standard needs them to stay fixed.
What about balloons typed as plain text?
They don't follow the BOM at all. Replace them with linked balloons.