Unlike most magnetic bit holders which use a single magnet to magnetize the driver bit, the SuperMag Bit Holder will save you time and hassle with a second “ring” magnet that surrounds the driver bit. The “ring” magnet pulls the screw head tight against the face, basically locking the screw in place. The adjustable collar threads onto the holder body for the perfect positioning of the second magnet and proper engagement of the driver bit. Designed to fit flat head screws and can be used with any ¼” hex shank - 1” long insert driver bits. Top portion made of Stainless Steel.