Connecting backing to the fly line is the common Albright application. The knot wraps the thinner line around a loop of the thicker one, so it still holds when the two lines are very different in diameter. That is exactly the situation at the back of the fly line, where thin backing meets the thicker line.

• A. Backing to fly line
• B. Attaching a reel foot
• C. Locking a rod ferrule
• D. Drying a fly

Answer: A. The other options are not joins between two lines. A reel foot is fixed to the rod seat, not knotted on; a rod ferrule is a joint in the rod itself; a fly is dried on a patch or in a box, not with a line-to-line knot.

The Albright is worth knowing for that backing-to-fly-line join and for other places where a fine line has to hold on a coarse one. It is not a tippet-to-fly knot or a leader-to-tippet knot for similar diameters; those are different jobs. Tie it with the wraps neat and tight, and it will pass out through the guides under load.

Source

From Animated Knots: Albright knot; terms follow the FFI Fly Casting Definitions.