Used for attaching metal to heavy section steel (Max. 12mm) without the need to pre-drill a hole. Exterior plating gives a reliable and durable corrosion resistant coating which resists 500 hours salt-spray" Thread Dia. mm: 5.5 Length mm: 55 Head Type: Hex Fixed Washer Dia. mm: 12.00 Point Type: Self-Drilling No.5 Socket Size mm: 8 Finish: Exterior (Silver Organic) Material: Case & Core Hardened Carbon Steel Effective Thread Length mm: 36 Max Drilling Thickness mm: 12.0Size 5.5 x 55 - 100 Pieces Timco Metal Construction Heavy Section Screws - Hex - Self-Drilling in Silver