6-20 x 5/8 Hex Washer Head Self Drilling Screw Zinc Plated . A tapping screw with an integrally formed hex washer head , spaced or unified threads, and a #2 or #3 drill point. Designed to drill through steel. AISI 1022 or equivalent steel. Rockwell C50-56. Meets F.I.P.-1000.7 for torsional strength & drill speed. Meets ASTM A 510 for carbon steel manufacturing. Zinc plating meets ASTM B-117 for salt spray corrosion. Manufactured to SAE J78 for dimensional specifications.