Drill bit shank The name comes from the German "Stecken – Drehen – Sichern" (Insert – Twist – Secure). In German-speaking countries the back-formation "Spannen durch System" (Clamping System) is used, though Bosch uses "Special Direct System" for international purposes. The triangle shank is almost always made by machining three flats on round bar stock. It is intended as a minor modification of a straight shank, still allowing it to be held in a 3-jaw drill chuck, but allowing higher torque transmission and limited slipping. The Morse taper twist drill bits pictured right are used in metalworking. The full range of tapers is
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