What a part number diagram is
A part number, model code or SKU split into ranges of characters, with each range labeled by what it means and what can appear there, joined to its label by a leader line.
The fictional part number PNC-240-RS-W, split into four ranges, with what each one means.
What it is doing
Most part numbers are built from segments. The first few characters are a series, the next a size, the last a color. Where those boundaries fall is a decision the manufacturer made, and the string itself does not reveal it. A part number diagram writes that decision down so that someone outside can read it.
There are only two things in it: ranges of characters mapped to meanings, and the values each range can take. Everything else on the page is just an arrangement of those two.
What it is good for
- A reader can work out a specification from a code. Someone can read the label on a unit in front of them and know what it is
- Fewer questions. "What is the difference between these two part numbers" answers itself with one picture
- Fewer wrong orders. With the options listed, a buyer can assemble the code for the thing they want
- It survives a handover. Numbering rules often live only in one person's head
Where it turns up
The "how to read the part number" section of a product page, the front of a catalog, the specification pages of a manual, ordering guides, internal design standards — anywhere the reader has to assemble or decode a part number themselves.
Things it is mistaken for
| Looks similar | Difference |
|---|---|
| A product configurator | That builds a part number from choices. A diagram explains; it is not a form, and it goes on paper and into a PDF |
| A bill of materials | A list of the parts a product is made from. A diagram is about the characters, not the components |
| A model or class diagram | Diagrams used to design software. Different thing entirely |
| A numbering-rule table | The same information as a table. Tables work, but which character belongs to which item is faster to see in a picture |
Part number, model code, SKU, model number, type designation
The same thing goes by different names in different industries and companies. “Part number”, “model code”, “model number”, “SKU” and “type designation” are used according to each company's and industry's habits, and no officially unified definition of how they differ was found. Whatever the name, if it is a string whose ranges encode the specification, it is what this diagram is for — which is why the tool's field is labeled “Part number, model code or SKU”.
What makes a good one
- The ranges line up with the real part number — the characters above and the positions below agree
- It is clear whether the options are all of them or a sample; if a selection, say so in a note
- Conditions and exceptions sit in notes. "Over 10 m is made to order" inside a description makes it hard to read
- No crossing leader lines. Once they overlap, it stops being obvious which label belongs to which characters
- It stands alone. A diagram that needs the surrounding text breaks wherever it is pasted
How to make one
Usually by drawing the lines by hand, which means redrawing them every time a character is added. The tool on this site places them from the ranges and meanings you enter. There is a step-by-step guide, and worked examples to look at. If the part number itself is still to be decided, designing a part number comes first.
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