The BRISTOL KNOT  some times called the NO NAME KNOT is used to attach your main line to a heavy leader, say 20lb main line to an 80lb leader (trace). It is also useful for joining any loop knot to your reel line. Knots such as a BIMINI TWIST or a SPIDER HITCH or just a loop knot.

The BRISTOL KNOT is simple to tie and results in a very streamlined connection that passes easily over rod roller guides or through rod rings.

STAGE 1
Pass the leader (trace) line through the loop of doubled line

STAGE 2
Keeping your index finger hooked around the leader,
wrap the leader line five to seven times around the doubled line

STAGE 3
Pass the leader line end back through the loop formed by your index finger,
in the opposite direction from which it entered in step 1.
It's probably easier to understand by looking at the diagram above.

STAGE 4
Tighten the knot by moistening the lines with saliva and pull on
both ends ends of the tied line.
Trim back the leader line,
which should protrude at a 90 degree angle.