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 gas of sheet metal than any other self-piercing type. Malco® Zip-In® Sheet Metal Screw, Self-Piercing, #8 Thread, 3 in Overall Length, Hex Washer Head, Slotted Drive, Zinc Plated, Tapered Point, 1/4 in Head, Double Thread, 1/2 in Thread Length