To connect 2 units, we put flap into pocket.
There are many ways to design flap and pocket.

Sonobe-style Unit

For Sonobe-style unit, we depict as following:

  f   /
  .   -
.52 /|\
154 \|/
3   -
f   /

The common methods are

• Straight - flap is put into pocket on the left (1).
• Tuck-up - flap is bent to insert into pocket on the top (2).
• Tab - flap is long under pocket to wrap around spike (1 → 3).
• Hook - flap is hook into pocket on the right (4).
• Clip - flap is clip on the middle bent (5)

Triangle-leg Unit

For triangle-leg unit,

f/\ /\p
   |
   |
p\/ \/f

Flap and pocket share the right triangle shape,
they are insert and bent to hold together.