Dependence of rotational properties on the orbital period. Top: Rotational period vs. orbital period for SB1s (left) and SB2s (right). The y-axis of Fig. 16 is inverted in order to preserve that faster (slower) rotating stars are plotted up (down). The vertical long-dashed line separates close and wide binaries. The solid diagonal line labelled ‘sync’ marks equal periods, as required for synchonised rotation, whereby an inclination i = 30° of the rotational axis shifts the data points from this line by a factor of 1/sin(30°) = 2 to the dotted inclination line labelled ‘i = 30’. The two SB2s below the dotted inclination line indeed have known i_orb < 20° (HD 048099 and HD 167771). For SB2s, the components are connected with a vertical dotted line; for most wide binaries at P_orb > 10 d, P_rot differs strongly between the components but the difference reduces and disappears for close binaries. Middle left: Ratio of P_rot of the binary components vs. P_orb; the horizontal lines mark the median in each P_orb range. Middle right: P_rot vs. P_orb for those 53 SB2s with known inclination of the orbital axis i_orb; P_rot is corrected for inclination assuming parallel orbital and rotational axes. The solid and dotted diagonal lines mark the synchronisation range with a width of 30% and a factor of 2, respectively. The green triangle marks the range above the sync line discussed in the text. Bottom left: v sin i vs. P_orb for the 53 SB2s with known i_orb. Bottom right: v_eq vs. P_orb after correction for the inclination.