Abstract
Using Monte Carlo techniques, the critical Binder cumulant U* of isotropic nearest neighbour Ising models on square and triangular lattices is studied. For rectangular shapes, employing periodic boundary conditions, U* is found to show the same dependence on the aspect ratio for both lattice types. Similarly, applying free boundary conditions for systems with square as well as circular shapes for both lattices, the simulational findings are also consistent with the suggestion that, for isotropic Ising models with short range interactions, U* depends on the shape and the boundary condition, but not on the lattice structure.