Bracing and flange braces are structural, not optional extras. Rod or angle cross-bracing in the roof plane and in selected wall bays carries longitudinal wind load along the building’s length back to the foundations. Removing a braced bay to fit a door is one of the most common site changes and one of the most dangerous, because the load path it carried does not disappear with it and there is rarely an obvious alternative. Flange braces are small angles connecting purlins and girts to the inside flange of rafters and columns, preventing the compression flange from buckling sideways under load. They look inconsequential on a drawing and they are not, and they are also among the members most often omitted by an erection crew working quickly. Connections tie the whole system together: knee joints, ridge splices and rafter splices are almost always bolted end plates with factory-drilled holes, and bolt grade matters, since high-strength bolts in moment connections may require controlled tensioning and inspection. Substituting a lower grade because it was on the shelf is a structural change rather than a procurement one. Sheeting fasteners belong in the same category, because screw type, spacing and washer selection carry wind uplift into the secondary framing, and under-specified fasteners fail before the frame does. For the wider system these members sit within, see [pre-engineered steel buildings](/pre-engineered-steel-buildings).