More details about the The Double Surgeon's Knot
Uses: The Double Surgeon's Knot is used to join two lines of moderately unequal size, e.g., a tippet to a leader. Formed as a Double Overhand Knot, it is easy to tie.
The Double Surgeon's Knot allows you, with the same leader, to select the size of tippet to suit the size of the fly. It is usually used to join two pieces of monofilament.
Tying it: The Double Surgeon's Knot can only be tied with a tippet as the entire length of the tippet has to be passed through the overhand knot twice. After forming the knot, carefully set the knot by pulling on all four ends.
Alternative: As an option, the two lines can be passed through the overhand knot a third time to form the Triple Surgeon's knot.
Advantages: The Double Surgeon's Knot is one of the easiest knots to learn and is an excellent knot to join two lines of moderately unequal size.
Disdvantages: It is rather bulkier than the Blood Knot and creates a slight angle in the line.