Square knot
The reef knot. Joins two ends of the same rope — and unties with one pull.
What it is
The square knot (reef knot) joins two ends of the same rope, or secures a bundle. It lies flat, holds tight, and unties with a single pull on one end.
How to tie it
1. right over left, then under 2. left over right, then under 3. pull — the ends lie parallel, not crossed
When to use it
Reefing a sail, tying bandages, bundling, shoelaces (it's a slipped square knot). Never use it to join two ropes of different size — it'll slip.