Different periodical Frequency Selective Surfaces (FSS) whose unit cell are the Split Ring Resonators (SRR) or related geometries and their corresponding complementary screens were studied. This kind of FSS, sometimes called metasurfaces, have the advantage of avoiding secondary gratting lobes because of the small electrical size of the unit cell. The main aim of this paper is to investigate the effects of the metal thickness for these FSSs. it was found that the quality factor decrease for unconnected elements (strips) and increase for connected elements (slots). Besides, as the thickness increases, the resonance frequency decrease for the case of unconnected elements while increases for connected elements. These facts have been demonstrated by full wave simulations and a theoretical model is currently been developed.