Mag Drill Cutters
Also known as an Annular Cutter, Core Drill, Core Cutter, Broach Cutter or Trepanning Drill.
Invented in 1973, by Mr. Dough Hougen. These Mag Drill Cutters are, per hole, cheaper than the same sized Twist drills. With the ability to be resharpened a single cutter can drill over 10 times more holes than the equivalent Twist Drill.
The only downside to these cutters is that they have to drill a through hole, due to the hollow nature of the cutter they cannot drill blind.