Malco Zip-in Screws are known for their superior quality and is considered by many for being the best screw choice for HVAC metal duct fastening. The unique thread design and quality controlled manufacture spell the sheet metal screw difference. The screws are made with a sophisticated heat treat process which allows the screw to taper to a fine, sharp point without sacrificing critical point strength. A single starting thread is formed down to the very tip of the point and is the source of the screws penetrating power. A second thread above the point engages after initial penetration and drills in the screw double fast. The screws are faster driving, with a greater capacity for fastening heavier gauges of sheet metal than any other self-piercing type.