Square Washers are most often used in construction where building codes specify them as a structural component of framing and other subsystems, or in channels or square tubing. The square shape prvents them from rotating in the channel. Our square washers are manufactured with extra thick steel and stainless steel. Inner diameters are cut large to allow for hot dip galvanized bolts to fit through easily, and to also provide adjustment and alignment. 2, 2-1/4", 3" and 4" Square are all in stock, and manufactured in the USA. Plain steel square washers are suitable for any use where corrosion resistance is not required, and these washers are soft steel. Case hardened steel square washers provide extra strength because they are hardened, and then black oxide plated for both appearance and they do add a slight corrosion inhibition. Diamond square washers are manufactured from the diamond plate tread steel. By facing the diamondplate into the joint, they dig into soft materials and help anchor the washer in place. Soft steel hot dip galvanized offer the best corrosion resistance in our steel line. All Made in the USA.