Torsion misunderstanding

We seem to have strayed a long way from torsion, haven't we, bro? Anyway, complimentary vertical and longitudinal shears aren't even in the same plane...don't try to combine them! Let's forget the nailed section and look at a solid section b x h with a vertical shear force of V at that section. I is bh^3/12, Q max at the NA is bh^2/8, and the transverse shear stress at the NA is VQ/Ib = 1.5V/bh. There is also a longitudinal shear stress of the same value that acts along the longitudinal axis of the beam. But you don't design the beam for both stresses, just one will do, OK??