ok, those thingamathingies aren’t my thing…
but ! this trick is as ingenious, simple, quick and cheap as it gets. if we abstract the thingy for a moment and look for other potential uses, the fly line stopper, single, double, triple (and eventually in different colours to be effective in varied light conditions) in itself can be used as an adjustable sighter/indicator for Euro or sight nymphing or even as a take indicator for dry flies when there’s a lot of natural flies on the water and we’re not so sure if we’re tracking our own imitation or a natural.
i’ve been using the same nail-knot method with fluo-coloured nylons such as Amnesia red for years to be able to track parts of long leaders in complex currents and can see how the fly line trick will make tracking easier as it should stay on or closer to the surface, specially once floatant is applied. for sure something to try out.
pretty much all of us have old fly lines hanging around so this is a really good way to recycle them.
as for the nail-knot tool, i almost always have one on me but it’s not a necessity as it can very easily be done by hand with Gary Borger’s ‘Nail-Less Nail Knot’.
note that these hold on better on level lengths of line than on taped ones. have fun experimenting !