This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The bit of this countersink, Fig. 400, is in the shape of a hollow eccentric cone, thus scouring a cutting edge of uniform draft from the point to the base of the tool, and obviating the tendency of such a tool to lead off into the wood at its cutting edge, and to leave an angular line where it ceases to cut. It works equally well for every variety of screw, the pitch of the cone being the same as the taper given to the heads of all sizes of screws, thereby rendering only a single tool necessary for every variety of work. It cuts rapidly, and is easily sharpened by drawing a thin file lengthways inside of the cutter. By fastening the gauge at a given point, any number of screws may be driven so as to leave the heads flush with the surface, or at a uniform depth below it. The gauge can be easily moved or detached entirely, by means of the set-screw.