A unique thread design and quality controlled manufacture spell the Zip-In difference. Zip-In's sophisticated heat treat process 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 Zip-In's penetrating power. A second thread above the point engages after initial penetration and drills in the screw double fast. Zip-In screws are faster driving, with a greater capacity for fastening heavier gauges of sheet metal than any other self-piercing type.