Drill bit shank from 0 to 7. The Morse taper allows the bit to be mounted directly into the spindle of a drill, lathe tailstock, or (with the use of adapters) into the spindle of milling machines. It is a self-locking (or "self holding") taper of approximately 5/8" per foot that allows the torque to be transferred to the drill bit by the friction between the taper shank and the socket. The tang at the end of the taper is only for ejecting the drill bit from the spindle, with the aid of a drift. The arbor of a drill chuck is often
Drill bit as the bit is either establishing the "center" of a hole or making a conical hole for a lathe "center". However, the true purpose of a center drill bit is the latter task, while the former task is best done with a "spotting drill bit" (as explained in detail below). Nevertheless, because of the frequent lumping together of both the terminology and the tool use, suppliers may call center drill bits "combined-drill-and-countersinks" in order to make it unambiguously clear what product is being ordered. They are numbered from 00 to 10 (smallest to largest). Center drill bits are meant to