The disulfides and diselenides of the second and third row transition metals from Groups 4 through 7 have been studied for their ability to function as solid lubricants. These materials have similar layered crystal structures. This work has shown that only those with the MoS2 type structure and a minimum value of the axial ratio of lattice parameters have inherent lubricating ability. The minimum axial ratios for low sliding friction have been experimentally established as 1.93 and 1.96, respectively, for second and third row transition metals. A rigid sphere atomic model shows that low friction sliding cannot take place unless the axial ratio exceeds 1.87. Formation of binary solid solutions between the chalcogenides of Group 5, 6 and 7 transition metals shows that the MoS2 type structure is stabilized at an average metal group number of 6, and that good lubricating properties are obtained when the axial ratio exceeds the minimum values previously stated.