Use Discount Strut Accessories 5/16" x 11/32" 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 = 5/16"; Hole = 11/32"