Blue zinc-plated. Fixes into various types of masonry or wood without the need to use a plug. Bites its own thread on fixing for a secure installation. Pre-drill a 6mm pilot hole with a drilling depth equal to the length of the screw, plus an extra 10mm. Multi-Head Countersinks Screw Head Flush Single Thread with Ground Serrations for Fast & Accurate Driving Zinc-Plated & Blue-Passivated Hardened Steel Construction WIROX Coated Fully Threaded Screws Direct into Masonry, No Plug Required Deeper Recess for Stronger Bit Hold Fast Time Saving Application Multi-Head Countersinks Screw Head Flush Single Thread with Ground Serrations for Fast & Accurate Driving Zinc-Plated & Blue-Passivated Hardened Steel Construction WIROX Coated Fully Threaded Screws Direct into Masonry, No Plug Required Deeper Recess for Stronger Bit Hold Fast Time Saving Application