Viscosity corresponding to the additional mechanism for the internal transport of angular momentum during the subgiant phase as a function of the radius of the star normalized to the radius at the end of the MS. Dots indicate the values determined in the present study. Open triangles correspond to the values of the 1.25 M_⊙ models studied in Spada et al. (2016), which are used as approximate models for stars B and D (red and blue triangles respectively, see text for more details).