Defining mesoscopic length scales for deformed nanostructures requires a close coupling of theory and experiment. One approach to this is to mechanically probe single crystal nanospheres of the same size that can be evaluated computationally. This involves analyzing dislocation nucleation and its corresponding yield instability represented by either a displacement excursion or load drop. We propose that the external work necessary to create the instability can be accounted for by idealized prismatic loop punching when the associated surface work, dislocation work and stored elastic energy of the loop are accounted for. This is shown both for experimentally compressed silicon nanospheres and theoretically simulated nanoindentation of silver (from work of Christopher, et al., 2001). For relatively large cumulative strains in a freestanding aluminum nanostructure, it is shown that Taylor hardening can predict flow stress behavior consistent to first order with atomistic simulations.