• Fundamental twinning mechanisms of FCC crystals were studied by micromechanical testing. • Single-slip based twinning mechanism are predominant in sub-micron pillars. • The size scaling for dislocation slip and twinning is identical. • A secondary twin type is observed in multi-slip activation cases. • The lower bound for the critical twinning shear stress for the Cantor alloy is around 130 MPa. Deformation twinning is an important deformation mechanism for low stacking fault energy face-cente