Just one variation of the versatile Uni-Knot "system," the Double Uni is used for joining two lines. It works best when connecting lines of similar diameter, be it mono-to-mono (splicing) or mono-to-fluorocarbon (line to leader). This knot can also be used to connect a less-visible fluorocarbon leader to braided line. The braid is sometimes doubled if its diameter is much smaller than the fluoro, and the number of turns on the braided side of the knot should be at least doubled in this case to prevent slippage. Text and illustrations by Tom Waters STEP 1: Lay the two parallel line ends in opposing directions with at least six inches of overlap. Form a two-inch Uni-Knot circle with one line end, crossing the two lines about mid-way of the overlapped distance. STEP 2: Pinch the loop against the line and with your other hand make six turns with the tag end around both lines (12 turns or more with braid), passing the tag through the loop each time. STEP 3: Following the last wrap, pull the tag end and tighten the wraps around the standing line. That will leave you with almost six inches of the standing line for repeating the same process. STEP 4: Again form a two-inch loop with the remaining line, making the appropriate number of turns around both lines, and passing the tag end through the loop each time and then pulling it to tighten the wraps. STEP 5: Moisten both knots and pull the standing lines in opposite directions to slide the two Uni-Knots together. At this point, snugging the knots tightly to each other is essential for maximum strength.
STEP 6: Closely trim tag ends. This knot works well for lines up to at least 30-pound test, with a holding strength of about 90%. If you want closer to 100% reliability, double over the tag ends of both lines before tying the knot.