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. Malco® Zip-In® Sheet Metal Screw, Self-Piercing, Measurement System: Imperial, #8 Thread, Hex Washer Head, Slotted Drive, Zinc Plated, 1/4 in Head, Double Thread, 1 in Thread Length