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Now consider an external load applied to the system. For instance, assume that a tensile load Lx is applied to the bolt where the face of the nut contacts the joint (Fig. 6). This interface is the "loading plane." As the bolt is pulled, the load on the bolt, FB, is increased while the clamp load on the joint, FI. is decreased. When the system was first assembled, these two loads were equal to the preload Fp. As the external load is applied to the bolt, the joint starts to return to its unloaded thickness along the elastic curve. At the same time, the bolt is elongated by the combined force of the joint "pushing'' out on the nut and the external load. Note that since the nut stays in contact with the joint while the external force is applied, the changes in deflection in the bolt and the joint are equal. In other words, the bolt gets longer by the same amount the joint becomes thicker.