The FG knot is the gold standard for joining braid to a leader. Instead of tying two knots together, the braid is woven tightly around the leader, producing a connection that is remarkably thin and remarkably strong. That slim profile is the whole reason to learn it: it passes through the rod guides on the cast with barely a click.
When and why to use it
Use the FG whenever you cast a leader knot through the guides and want distance and reliability, surf fishing, tuna popping and jigging, albie and striper work with a long leader. It is the connection of choice on a surf setup or a popping setup. The catch is difficulty: it is fiddly to learn, so practice it at home before you rely on it in the dark or in a blitz.
How it works
You hold the leader under tension and weave the braid back and forth around it in a series of alternating wraps, then lock the weave down with a few half hitches over both lines and trim. Done right, the wraps bite into the leader and the knot cinches into a slim, bombproof splice. A tool or a set hand position for tension makes it much easier.
Tip Learn it on the couch, not on the beach. The FG rewards muscle memory, so tie a dozen at home until your hands know the weave, then it becomes quick even in the wind and the dark when it matters most.