A device is described for applying known static strains to strain gauges under extreme temperature environments. The essential part is a constant strength cantilever beam used in such a way that the mechanical properties of the component parts need not be accurately known. The location of the strain gauges on the beam is not critical since strain is constant along its length. Conditions are given for which errors caused by thermal expansion can be eliminated. Measurements of the strain sensitivity of constantan wire gauges are given at temperatures between 4 and 300°K.