Disclaimer: this is a non disclosed feasibility study. It documents the requirements, design and test process of a potential future product.
Specification
- Character size = 1mm
- Washer diameter = 24mm (M8 DIN 9021 8,4 A2 Edelstahl InnenØ x3 ISO 7093)
- One ring can hold 54 characters. BIP-39 (english) word list max word length = 8
- 6 words x (8 letters + 1 space) = 54 characters
- 12 word seed fits on one washer side, 24 word seed double sided.
- 3rd inner ring can hold 27 characters, can be used for additional info
Test phrase
- 53 characters, any of 26 letters at least once, bitcoin themed:
- BITCOIN MARKET WAVES DOING QUICK JUMPS OVER HAZY FLUX
Quality Check
- All character outlines and details visible (e.g. O,Q)
- No character overlap
- Character shift < 20%
- Character imprint repeatable
Seed phrase form
Printable single A4 form: one column per washer side, 12 words each. The jig has three holes: OUT stamps the outer ring and IN the inner ring, 6 words each, 9 positions per word. A 24-word seed uses both sides of the washer.
ODD stamps the innermost ring. Its characters sit so close together that only odd positions (1, 3, 5 …) are stamped, so use it for a short label that marks the washer side: 1/2 and 2/2, or for a multisig wallet A1, A2, B1, B2, C1, C2 (key A, B or C; side 1 or 2).
Fill the form in offline, check every word against the BIP39 list, and destroy it after stamping. Never photograph it or store it digitally.
ToDo
- Durability test of jig, >10 seeds without damage, wear
- Durability test of washer (rust, heat)
- Different washer types (back side, front side)