8-18 x 1 5/8 Phillips Modified Truss Self Drill Screw Zinc Plated . Phillips modified truss head tapping screw , 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.