On the basis that the dominant: source of the maximum load-size effect for an uncracked brittle structure is deterministic, it can be associated with the formation of a damage (fracture process) zone at a free surface. By modelling this damage in terms of the cohesive zone description, and associating the maximum load with the attainment (at the free surface) of an elastically calculated effective tensile failure stress, earlier work has shown that the effective stress is critically dependent on the applied loading-included stress gradient beneath the surface, with the effective failure stress increasing with the steepness of the stress gradient. The earlier considerations have been extended in the present work to assess the effect of a small surface flaw (crack) on the effective failure stress, and to show how the small flaw tolerance, as manifested by the reduction in effective failure stress, depends on the stress gradient, flaw depth and material fracture parameters.