From DT Online
Features and Applications
Some force is required to push them through the timber, so are best suited to use in a Drill Press. Since they locate mainly on their rim, with only a small central point, it is possible to drill a series of overlapping holes (e.g. to clear the waste from a Housing Joint).
Their name is derived from their inventor, Benjamin Forstner, an American gunsmith who patented the design in 1874. Saw Tooth variants are now available which cut a little faster and are more suitable for drilling into End Grain.