Essential tool to tie fly line and tapered leader.
Splice the tapered leader to the fly line, then use pipe included to create nail knot with small bundle to avoid entangled with top guide.
When drawing a line from the top guide or hauling in a fish, it becomes much comfortable just by eliminating the interference with the guide by minimizing the bundle.
Small magnet on the tip of nail knot pipe is convinience for picking up small flies from compartment box, It also can be used to temporary hold flies when switching flies.

Be careful not to warp the needle when splicing the tapered leader to the fly line core. It will lead to needle breakage and damage.
If the nail knot pipe is crushed, it may not be possible to store the splice needle.
After use, push the nail knot pipe to the root of the splice needle, and be careful not to lose it by dropping it.