1/4-20 x 3 3/4 Phillips Flat Head Reamer with Wings Zinc Plated . Phillips flat head tapping screw , spaced or unified threads, and a #3 or #4 drill point. Designed to drill through steel to attach wood to metal. 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.