Designing a part number that reads well
The other guides start from a part number that already exists. This one is the step before. It is for the person about to define a scheme, or to tidy up one that grew on its own, and it is about one thing: a number that someone else can decode later. One invented part number is worked through from a bad first draft to a usable one.
A part number is a sentence
A good part number states one fact per range: which family, what size, how it mounts, what color. The reader goes left to right, from the broad classification down to the detail.
So the order is stable facts on the left, changeable ones on the right. A product family lasts for years; colors and accessories get added every season. The revision mark goes last. A fact on the left changes only when the thing has become a different product.
Growing one invented part number
Say we are making an outdoor temperature sensor. The first draft is the name it had during development:
TS2-OUT-NEW
Three problems. TS2 — is that the second generation of temperature sensor, or two
channels? Nobody decided. OUT means outdoor, but when an indoor model comes, is it
IN, or do we split by ingress rating instead? Not decided either. And
NEW will be a lie next year.
One fact per range, and it comes out like this:
TS-A2-W67-M12-R1
| Range | Fact | Options today | How it grows |
|---|---|---|---|
TS | Family (temperature sensor) | TS | Almost never |
A2 | Sensing method and generation | A1, A2 | One every few years |
W67 | Ingress rating (IP67) | W54, W67 | Per application |
M12 | Connection | M8, M12, CB (flying lead) | When a customer asks |
R1 | Revision | R1 | With every compatible change |
The vague word “outdoor” is gone, replaced by an ingress rating, which can be measured.
“NEW” became a revision mark: when R2 ships next year, R1 is still true.
This part number is drawn in the examples.
The five rows of the table become five items. A2 is the one exception to the rule above —
it holds two facts, the method and the generation — and that shows the moment you have to write its heading.
Keep the widths even, and leave room
Ranges that carry the same fact should be the same number of characters across
the family. When connection is M8 in one product and M12 in the next,
columns drift in a spreadsheet and the eye stumbles for a moment. The table above has that
flaw (M8 and CB are two characters, M12 three); the alternative is to fix three from the start —
M08, M12, CBL. Which you choose matters less than deciding
and keeping to it.
Even if a range has two options today, decide now how many it may hold. One letter gives 26; two alphanumerics give over a thousand. A one-character range that was “enough for now” can run out later and force a new scheme for the whole family.
Characters to avoid
- 0 and O, 1 and I and l. Hard to tell apart in print and on screen, impossible over the phone. Use one of each pair, or neither.
- Full-width letters and digits. Mixed with half-width ones, a search or lookup may not match, depending on the system; check in the one you will actually use. This tool notices them in the part number and says so — half-width characters keep the spacing even.
- Anything outside letters, digits and punctuation. A Japanese character in a part number can turn to garbage in a partner's system abroad. The tool flags these too, as characters the diagram's typefaces do not carry.
- Mixed separators. A hyphen here, a space there, a slash somewhere else, and whoever types it has to guess. Pick one.
Test whether it can be read
Whether the number really decodes is something its author cannot judge. Make one diagram, hand
over the diagram alone, and ask someone who does not know the scheme what
TS-A2-W54-CB-R1 is. “Lower ingress rating, flying lead” is a pass. Wherever they
stall is where either the ranges or the headings need work.
While making the diagram, the tool's checks help too. An item with an empty heading, or an option with no code or no description, is listed as something to do; a heading used by more than one item is reported as a duplicate. A duplicate usually means two ranges are secretly the same fact.
Write it down once it is decided
A scheme that lives in one person's head is not a scheme. Save the diagram as JSON, one per family, and it becomes the thing you hand to the next person. When a revision adds a range, open that file, add the item, save again.
For what the diagram is, see What a part number diagram is; for the steps, How to make one.
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