A simple bond model of the optical second-harmonic (SH) response frominterfaces, which assumes a single axial component for each bond, istested by comparing the response from different step structures at theSi–SiO2 interface. The response of native-oxide-covered vicinal Si(111), offcut by3° towards , is compared with previous work on similar samples, but offcut by5° in the opposite, , direction. The two offcuts have different step geometries, but the same terrace structure at theSi–SiO2 interface, while the bulk quadrupolar contributions from the two offcuts are related bysimple geometric factors, thus significantly constraining the number of adjustableparameters. The bond model is tested against experiment for the eight sample rotationplots obtained by permuting s- and p-polarization combinations. The constrained fit isfound to be too poor to justify the extraction of quantitative information. Kleinmansymmetry is shown to be a necessary, but not sufficient, condition for determining whethersuch a simple bond model can be applied, quantitatively, to the SH response frominterfacial structures. It remains possible that quantitative information may beobtained from axial bond models by including local field effects in a simple way.