Self-drilling screws for steel have traditionally been used for joining secondary or non-structural structural elements, which are thin cold-formed profiles or parts made of thin steel sheets. These joints have been studied mainly in terms of strength, leaving aside in most cases the characterization of the component's stiffness. In addition, studies have focused on joining sheets with thicknesses less than 3 mm, observing a group effect on strength, which is not proportional to the number of screws [1]. However, there are some commercial self-drilling screws that allow drilling of up to 12 mm and can be used in main joints of some structures. This study examines the influence of screw diameter and number of screws on the stiffness and strength of self-drilling screws under shear joining relatively thick sheets. Two types of screws, with diameters of 5.5 mm and 6.3 mm, were experimentally tested under identical conditions studying the effect of the number of screws (1, 2, 3, 4 and 6 screws) on the strength and stiffness of the connection. The work is completed with a FEM simulation validated with the experimental results. To do so, it was necessary to obtain the actual yield stress and tensile strength of the self-drilling screws indirectly by means of the Vickers hardness test, since the use of standard tensile tests was impossible with the available resources. The main results were that the group effect can be practically neglected for parts with a thickness greater than 3 mm and that the “self-drilling screw” component, understood as the screw and its immediate contour, was characterized for use in component-based analytical models such as the one previously proposed by the authors [2].