A specialized drill bit designed to bore perfectly centered pilot holes for hinge-mounting screws, shown below. The bit uses a standard twist drill inside a retractable spring-loaded sleeve. A tapered end on the sleeve fits into the countersink on a hinge screw hole to automatically center the bit when you press the sleeve against the hinge. Commonly referred to as "Vix" bits (the brand name of the original version), self-centering bits come in various sizes to accommodate different screw gauges.