Rules should be simple. There shouldn’t be many of them, and they should be easy to remember. And in mechanical design, rules should be beautiful. Ugly rules are bad rules. A beautiful rule is a 10 mm base thickness for a tray. 7.62 mm would be an ugly thickness. Rules exist to be broken, but they should only be broken when it serves a purpose. Breaking rules just for the pleasure of destroying a beautiful system is like trampling fresh flowers growing in a forest clearing.

RULES:

• Basic cell dimensions: 80 × 80 × 10 mm
• The space for magnets (or clips) starts 8 mm from the tray wall (8 mm is 1/10 of 80. That’s a nice rule).
• The magnet slot is 8 mm long, 4 mm wide and 9 mm deep (those were exactly the magnets I happened to have at home over the holidays. Not every rule has to come from deep research; some are happy accidents).
• Wall thickness at the magnets: 1.5 mm
• The trays have 4 mm chamfered corners. I don’t fully know why yet, but I’m sure it will be important. And it looks much better.

The modifiable space is a 66 × 66 mm square inside the tray. This comes from offsetting the tray’s outer dimensions by 7 mm, leaving an untouched rim for magnets and other mounting features around the entire tray. 6 mm was too thin, 8 mm was definitely too thick.

That’s all. And yet, that’s everything. A handful of rules to brand the wicked and reward the righteous.