Serial numbering schemes for hardware prototypes

Published 18 September 2026

A serial number looks like a trivial decision until you’re three revisions in and discover that P2-B-07 and P2B7 refer to the same board. Here’s how to pick a scheme once and never think about it again.

The goal: unique, short, boring

A good prototype serial is:

• Unique within its scope (usually the design).
• Short enough to fit on silkscreen or a small label and be read aloud.
• Stable. It never changes, even if the board is reworked to a different revision.
• Boring. It carries as little meaning as possible.

That last point surprises people. It’s tempting to encode revision, build date and assembly house into the serial. But boards get reworked from rev A to rev B, builds get re-dated, and assemblers change. When the encoded information goes stale, the serial becomes actively misleading. Store that information as data about the unit, not in its name.

A scheme that works: prefix + counter

MC4-001
MC4-002
...
MC4-117

• Prefix: a short, fixed code for the design (MC4, SH2, BMS). Keep it to 2–5 characters.
• Separator: a hyphen. It’s easy to read and hard to confuse with other characters.
• Counter: zero-padded to a fixed width, so serials sort correctly as text. Pick a width you won’t outgrow: three digits covers most prototype programs; use four if you expect more than 999 units.

The counter runs continuously across revisions. Rev A might be 001–012 and rev B 013–040. That’s fine, because the revision is recorded separately.

Characters to avoid

Avoid characters that are easily confused when handwritten or printed small: O/0, I/1/l, S/5, B/8, Z/2. If you need letters in a counter, use a restricted alphabet such as Crockford’s Base32, which omits I, L, O and U.

Batches

Boards usually arrive in batches from a panel or an assembly run. Allocate serials for the whole batch at once so there are no gaps or duplicates when two people log boards at the same time. In Proto Tracker, you enter the first serial and a quantity, and the rest are generated with the padding preserved. Clashes with existing serials are rejected before anything is created.

Labelling

• Silkscreen a serial field (a blank white box) on every prototype layout. It costs nothing and survives handling better than stickers.
• Add a QR code that encodes a link to the unit’s record, not just the serial. Scanning should take you straight to its history.
• Put the label somewhere visible when the board is installed in its enclosure or test fixture.

Summary

Use a design prefix, a hyphen and a zero-padded counter. Encode nothing else. Keep revision, dates and rework as data. Label every board physically. Then read how to track PCB prototypes for the rest of the system.