it’s not really a new twist as i found this on Gary Borger‘s site years back but this not-so-well-known knot’s particularities common to almost every knot are well worth bringing back up.
what we’ll typically see in knot diagrams, animated diagrams and videos is that a given number of turns of the tag end should be used to form the knot.
that’s all fine and well but that doesn’t mean that the line diameter used in the demonstration is the same diameter as what we’ll be using ourselves in a given situation.
since we normally don’t want our knots to slip, when tying them we need to keep in mind that a thinner diameter line needs more turns to not slip and inversely, the breaking strain tolerance of bigger diameter lines can actually be diminished by too many turns. without having any measuring tools to ‘scientifically’ turn those last statements into facts, it’s pretty easy to test this out yourself at home.
to sum it up, my guess and personal conclusion is the thinner line needs more surface contact area and the thicker material can suffer from not seating properly due to it’s inherent stiffness compared to thinner lines. that last part may or may not be correct but what i’m certain of is with thicker lines, the more turns we use, the more visible and proportionately bigger gaps there are in the knot and that’s not good.
another point that relates to the stuff above, and in our case of the standard Blood knot, is that the typical demonstration of this knot says to use five turns on both sides and that too is all fine and well but it still doesn’t take into account mono diameter and also, that we’re usually joining two pieces of mono that have different diameters.
while that standard knot may hold without failing with mono diameter jump ups or downs of one size (ex: 4x to 5x), the connection that has already been weakened by doing so will start to really suffer if we increase diameter difference when connecting a two size difference as 4x to 6x and even worse if we connect 4x to 7x.
ok, the 7x example is quite extreme and of little practical use (and of course weak) but that example is to give you an idea that the standard knot would give an asymmetric final knot if tied as per equal turn instructions.
now, as a brilliant and simple solution to remedy the nasties above, Gary devised the 5/7 Blood knot seen here. it’s still the same knot in it’s basic construction but the thinner materials gets two extra turns resulting in a better grip. it doesn’t slip and the knot becomes symmetric again and regains all of it’s efficiency where it really matters: in the ‘real world’ of fishing.