A light duty metal to metal screw with a square recess used for interior applications. Fire Classification: A1" Thread Dia. mm: 4.2 Length mm: 13 Head Type: Pan with Serrations Recess Type: Square Point Type: Self-Drilling Driver Bit Size: SQ2 Finish: Zinc Material: Carbon Steel Max Drilling Thickness mm: 3.0Size 8 x 1/2 - 1000 Pieces Timco Metal Construction Sheet & Stud Screws - SQ - Pan - Self-Drilling in Silver