Square head bolts were the industry standard prior to hex bolts gaining prominence. Square bolts are now most commonly used for aesthetic purposes to provide a rustic look in a new structure or to match existing fasteners in an older structure. Standard Thread Lengths Bolt lengths < 6″: Thread length = (2 X diameter) + 1/4″ Bolt lengths > 6″: Thread length = (2 X diameter) + 1/2″ Square Head Dimensions Bolt Diameter D F C H Body Diameter Width Across Flats Width Across Corners Height Max Basic Max…