Commensurability between inter-vortex distance and crystal lattice constant is investi-gated by angular dependent magnetization in very pure twinned and twin-free NdBa₂Cu₃O_y single crystals. With increasing temperature the incommensurate states split up and become finally com-mensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and discussed with respect to temperature, field,anisotropy, and twin structure.