The distribution of load on the threads of screws and the types of deformation affecting it have been investigated by means of extensometer measurements made on the outside of the nut. The types of deformation characteristic of concentrations of load on different parts of the thread were found by using a bolt carrying only a single turn of thread. At low loads the deformations of nuts with complete bolts closely resemble the effects of the artificial concentration of load on the base part of the thread, whereas there are marked contrasts with the effects of loads concentrated at the middle or at the free end. At higher loads a more uniform distribution is indicated. Similar conclusions follow from the application of an approximate method for deducing the distribution from the deformation measurements.
It is shown that the distribution is governed by (a) stretch and compression in bolt and nut, respectively, which are primarily responsible for concentration at the base; and (b) by bending of the thread, circumferential stretch (at the base), and contraction (near the free end) of the nut wall, which have comparable effects in reducing the concentration.