Use Discount Strut Accessories 1/2" x 9/16" Stainless Steel Flat Square Washers to fit into slots or channels, prevent components from rotating, & distribute heavy loads. The 304 stainless steel material is ideal for outdoor use, highly resistant to corrosion, & great for chemical or saltwater applications. Finish: ST304 Size: Bolt = 1/2"; Hole = 9/16"