5/8" x 5/16" (15.9 x 7.9 mm) box type Spreader Bar is made of .025 mil (.64 mm) thickness roll formed aluminum. Adds rigidity and strength to large size screens. Almost always installed across the mid-point of the screen's longest side. Installs with our Cat. No. WSC112 Spreader Bar Clips. Important Notes: Because of tolerances in coil stock and stretch in the roll forming process, stock thicknesses can range from the advertised thickness plus or minus .002" (.05 mm). This is standard in the industry.