Many proteins in the body are subject to mechanical forces in their natural context. Examples are muscle proteins or proteins of the cytoskeleton. Often a protein faces the challenge of refolding against a mechanical load. Although the unfolding of proteins under load has been extensively investigated, knowledge about refolding mechanics is still rare. This chapter develops a model that describes the effect of an external force on protein folding. The model can provide important help for the design of a single-molecule mechanical experiment. The chapter discusses how spacer length and elasticity, as well as probe spring constant, affect the observed results. In this context it also briefly discusses the difference between atomic force microscope and optical tweezers experiments.