Space is limited on a metal plate, so a clever feature of the BIP39 word list matters here. This guide is part of our metal seed phrase backups section.
The four-letter rule
The BIP39 standard says that its English word list was chosen so that the first four letters identify each word without ambiguity. So abandon can be stored as aban, and no other word on the list starts that way.
| Full word | Stored as |
|---|---|
abandon | aban |
ability | abil |
absorb | abso |
add | add |
zone | zone |
These are words from the public list, so they reveal nothing.
Why it helps
- Metal backups have limited room, and four letters fit in less space.
- Stamping a four-letter word takes much less time than a long one.
- Fewer letters means less chance of error when you punch.
Most wallets also autocomplete as you enter words, once you have typed the first few letters.
Words that look alike
Some words share their first three letters, and these need careful checking:
| Prefix | Words |
|---|---|
aba | abandon |
abi | ability |
cra | crack, cradle, craft, cram, crane, crash, crater, crawl, crazy |
con | Many, so check the fourth letter closely |
Fourth letters matter. A smudged or misread letter can be a different word, or an invalid word.
How to use it safely
- Check that you are using the English list. See how BIP39 works.
- Stamp at least four letters, and more if you have room.
- Add the word number, so that the order is clear.
- For a final check, confirm that each four-letter prefix matches your full word.
- Test your backup by restoring from the short form on your device.
Do you need to record the full word too?
No, but make sure that a family member could use the backup. Add a note to your inheritance instructions explaining that only the first letters are stored. Keep that note separate from your backup.
Now you are ready to stamp a plate or compare metal backup designs.