Phillips Flat Head Self Drilling Screw With Wings, #4 point: All Weather Coating
Coated for exterior use, these screws are designed for wood to metal applications. The wings ream the hole larger than the threads so the threads will not engage the wood. The wings break off when they engage with the steel, so then the threads may engage with the wood. Recommended that your steel be at least 1/8" thick for proper engagement. Measurement is over all length, drill tip end is about 3/8". A fastener that drills and taps its own hole during application.