In the case of the Dendera Zodiac, the 'thread' is putting in its 'proper place' (as we know nowadays), it is fixed to the fish's tails, and the peak of the pointed angle appearing below involves 'The Knot of Heaven', the fixed star named alpha
Piscium (al Rescha). What is so special about this astrological illustration, is that the presence of a pictogram with quadratic contour between the two fish bodies, which emphasizes the presence of the humid and fluidic quality. This pictogram
represents probably the Great Square of Pegasus (of course, in the reality, it is above the Pisces), and the stars that make up this square are Scheat, Alpheratz, Markab and Algenib.