Self-drilling screw for sheet metal - has tapering expander portion and parallel one both with fine thread

摘要

The self-drilling screw secures a wooden component to sheet-metal, being particularly for rafters to a roof base structure. It has a drill tip (5) and a spanner or screwdriver head (7) at opposite ends of the shank (4), with a parallel supporting thread (6) in between. The thread is preceded by a tapering expander portion (5), both having a fine thread of pitch between 0.7 and 1 mm. and base diameter between 4 and 6 mm. A washer (10) guided on the shank bears against the head underside. ADVANTAGE - Forms firm joint while reducing risk of overtightening.