Metric Annular Cutters
An annular cutter, much like the core drill and hole saw, cuts a groove in the metal at the periphery of the hole and leaves a solid core or coupon. They are used in magnetic drill presses with a pilot pin (drill) and most commonly have a "weldon" (universal) shank. Hougen and Jancy are both manufacturers who's brand name has become synonymous with this type of cutter. These are the metric sized versions.