Malco's 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. A unique thread design and quality controlled manufacture spell the Zip-in® sheet metal screw difference. Zip-in's® 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 Zip-in's® penetrating power. A second thread above the point engages after initial penetration and drills in the screw double fast. Malco's Zip-in® screws are faster driving, with a greater capacity for fastening heavier gauges of sheet metal than any other self-piercing type. For the best performance, use any Zip-in® Sheet Metal Screw with a Malco C-RHEX™ Cleanable, Reversible Dual Sided Hex Driver.