The size of a screwed fastener is first established by calculating the tensile load to be withstood by the screw and selecting a suitable screw to withstand the tensile load with the appropriate factor of safety or preload. If the joint is fixed using a nut and bolt then assuming the nut is selected from the same grade as the bolt there is little need to size the nut. The fastener manufacture sizes the length of the nut to ensure the screw will fail before the nut. If the screw fastens into a tapped hole then a check of the depth of thread engagement is required.