The universal building block which is an essential part of all atomic structures on (1 1 0) silicon and germanium surfaces and their vicinals is proposed from first-principles calculations and a comparison of results with available experimental data. The atomic models for the (1 1 0)-(16 x 2), (1 1 0)-c(8 x 10), (1 1 0)-(5 x 8) and (17 15 1)-(2 x 1) surface reconstructions are developed on the basis of the building block structure. The models exhibit very low surface energies and excellent agreements with bias-dependent scanning tunneling microscopy (STM) images. It is shown experimentally using STM that the Si(47 35 7) surface shares the same building block. Our study closes the long-debated pentagon structures on (1 1 0) silicon and germanium surfaces.